These are differentiated epidermal cells found flanking the dumbbell shaped guard cells; they help control the pore size. According to Edwards et al. Grass stomata, as described as early as 1881 (Campbell, 1881), have both a pair of dumbbell-shaped guard cells and associated subsidiary cells. The size of the stomata is controlled by a pair of guard cells. The plants that grow on the water surfaces contain their stomata in the upper epidermis. “Stomata” by AJC1 (CC BY-SA 2.0) via Flickr, Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things, Difference Between Stomata of Monocot and Dicot Plants, What are the Similarities Between Stomata of Monocot and Dicot Plants, What is the Difference Between Stomata of Monocot and Dicot Plants. Stomata of Monocot Plants      – Definition, Guard cells, Distribution of Stomata 2. In contrast, the GCs of dicots are kidney-shaped and form stomata that are scattered throughout the epidermis in a less orderly pattern. Stomata of Monocot Plants: The leaves of the monocots are rolled to reduce the exposed surface area to the sunlight. Guard cells make stomata. The subsidiary cells … The outer walls of guard cells (away from the stomatal pore) are thin and the inner walls (towards the stomatal pore) are highly thickened. Stomata of monocot plants are the tiny pores in the upper and the lower epidermis of monocot leaves, which are surrounded by a pair of dumbbell-shaped guard cells. “Maize stomata” by Umberto Salvagnin (CC BY 2.0) via Flickr 2. What is the Difference Between Dermal Vascular and... What is the Difference Between Eustele and... What is the Difference Between Protostele and... What is the Difference Between Conceptacle and... What is the Difference Between Stipules and Bracts, What is the Difference Between Lemon Grass and Citronella, What is the Difference Between Taffeta and Satin, What is the Difference Between Chinese Korean and Japanese Chopsticks, What is the Difference Between Comet and Meteor, What is the Difference Between Bacon and Ham, What is the Difference Between Asteroid and Meteorite. What is the Difference Between Stomata of Monocot and Dicot Plants      – Comparison of Key Differences, Key Terms: Amphistomatic, Bean-Shaped Stomata, Dumbbell-Shaped Stomata, Guard Cells, Hypostomatic, Lower Epidermis, Stomata of dicot Plants, Stomata of Monocot Plants, Transpiration, Upper Epidermis. How improved valves let grasses 'breathe,' cope with climate change 16 March 2017 This image shows the four-celled stomata found in grasses, featuring two dumbbell-shaped guard cells Grasses and dicots share differently regulated orthologous transcription factors. Major components of the guard cell wall in grasses include cellulose (red), mixed-linkage glucans (MLGs, gray), and pectins (blue). The main difference between stomata of monocots and dicots is the anatomy of the guard cells and distribution in the epidermis of the leaves. The main difference between stomata of monocot and dicot plants is that the guard cells of the monocots are dumbbell-shaped whereas the guard cells of dicot plants are bean-shaped. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. Stomatal development: focusing on the grasses. The narrow section connecting these two parts passes through an opening in the spinal column called the neural foramen. Over the past twenty years most studies of stomata have used the model dicotyledonous plant Arabidopsis thaliana. In dicots, they are kidney or bean shaped. The guard cells contain chloroplasts, whereas the other epidermal cells … Sequential and phylogenetic analysis of OSAs Apart from regulating gaseous exchange (as well as water releas… Since the stomata of monocots are equally distributed in both upper and the lower epidermis, the stomata distribution of monocots is known as an amphistomatic distribution. In grasses, the guard cells are dumbbell-shaped. In case of plants like water lily or aquatic plants, the stomata are absent, … Here, we identify a transcription factor necessary and sufficient for SC formation in the … In extant plants, the earliest stomata are found in the Bryophyta (but seen only in the spermatophyte phase) (Ligrone et al., 2012). ). Stomata of Dicot Plants      – Definition, Guard cells, Distribution of Stomata 3. The stomata of most plant species consist of two kidney-shaped guard cells, while stomata of grass species are formed by two dumbbell-shaped … In grasses, guard cells are dumbbell-shaped and are In contrast, dicots contain bean-shaped stomata, surrounding the stomata. 1B ). We use cookies to help provide and enhance our service and tailor content and ads. In grasses, guard cells are dumbbell-shaped rather than the more common kidney-shape. The hypostomatic distribution of dicot stomata helps to prevent the water loss by transpiration. Since the stomata of dicot plants only occur on the lower surface of the leaf, the distribution of stomata of dicot plants is known as a hypostomatic distribution. Grass stomatal complexes differ from those of dicots. Many kinds of tumors can be dumb… stomatal complex This is the combination of the pore, the guard cells… Monocots contain stomata in both upper and the lower epidermis of leaves. In the spine, dumbbell tumors consist of one part of the tumor inside the spinal canal and another outside the spinal canal. The guard ceils possess chloroplasts and regulate the opening and closing of stomata. general, there are only two broad classes of stomatal guard cells: the kidney-shaped cells found most plant species and the dumbbell-shaped guard cells found in grasses (Evert, 2006) (see Fig. Gas exchange between the plant and the atmosphere takes place through stomatal pores formed by paired guard cells. “Stomata: Structure, Number, Distribution and Type of Stomata | Transpiration.” Biology Discussion, 26 Oct. 2015, Available here. Epidermal Cell: Epidermal cells are usually tubular in shape, but that may vary depending on the place they are found in the plant body. Dumbbell = having the shape of a dumbbell (narrower in the middle than on each end) Tumor= an abnormal growth A dumbbell tumor is any tumor that is constricted in the middle, giving it the shape of an hourglass or dumbbell. They also facilitate transpiration, which helps the absorption of water from the soil and the transport of water through the xylem. All vascular plants have abundant stomat… Guard Cell: Guard cells are bean-shaped cells and found as pairs in such a way to form an opening called stoma. The outer walls of guard cells are thin and the inner walls are highly thickened. The development and patterning of stomata in the plant epidermis has emerged as an ideal system for studying fundamental plant developmental processes. Monocots contain dumbbell-shaped guard cells, surrounding their stomata. Stomata of Dicot Plants: The stomata of dicot plants are arranged in an irregular pattern. In most dicots and monocots the guard cells are bean-shaped. Stomata evolved in the late Silurian to early Devonian (Edwards et al., 1986, 1998) and are one of the key innovations in plant evolution. Two main types: 1. Therefore in the presence of excess sunlight, monocot leaves are rolled to reduce the surface area of the leaf, preventing the water loss. The epidermal cells surrounding the guard cells are modified to form subsidiary cells. 1. But, most dicot stomata of dicots occur in the lower epidermis. Here, we identify a transcription factor necessary and sufficient for SC formation in the … The dumbbell-shaped cells present in the epidermis of grass leaves are called guard cells. Most notably, grass stomata are formed from dumbbell-shaped guard cells (GCs) that are flanked by subsidiary cells (SC) which develop in parallel rows within defined and specific epidermal cell files. This ‘graminoid’ morphology is associated with faster stomatal movements leading to more water‐efficient gas exchange in changing environments. The dumbbell-shaped stomata of a maize plant are shown in figure 1. Stomata of Dicot Plants: Dicot plants contain most stomata in the lower epidermis. Monocot and dicot plants contain stomata in their leaves as well as in their stem. Each stoma consists of bean-shaped or dumbbell-shaped guard cells. (A) In grasses such as Oryza sativa, guard cells are dumbbell-shaped and stomata are oriented in the same direction in the leaf epidermis. (1998), stomatal structure is the most conserved of land plant vegetative characters, presenting similar morphology and architecture throughout ∼400 million years of plant evolution. By contrast, grasses have ‘dumbbell’‐shaped GCs that are intimately connected to their lateral neighbours, the subsidiary cells (SCs). The major role of stomata is to facilitate the gas exchange. We studied the molecular basis of GC action in the major cereal crop barley. Grasses form rows of dumbbell-shaped guard cell pairs flanked by subsidiary cells. Both grasses and dicots use epidermal patterning factor family signaling peptides. However, little is known about grass stomatal complex development. The shape of grass guard cells also helps to hasten stomatal response because the dumbbell form reduces the ratio of internal volume to surface area compared to alternative kidney-shaped guard cells. Here, we show that H (+)-ATPases are involved in the regulation of dumbbell-shaped guard cells. 1. Although this regulation is thought to be widely adopted among kidney-shaped guard cells in dicots, the molecular basis underlying that of dumbbell-shaped guard cells in monocots remains unclear. In grasses, a developmental innovation-the addition of subsidiary cells (SCs) flanking two dumbbell-shaped guard cells (GCs)-is linked to improved stomatal physiology. guard cells, signalling, stomata, subsidiary cells, water use efficiency. They help in transpiration. The main difference between stomata of monocot and dicot plants is that the guard cells of the monocots are dumbbell-shaped whereas the guard cells of dicot plants are bean-shaped. Grasses (Poaceae) form morphologically innovative stomata, which consist of two dumbbell‐shaped guard cells flanked by two lateral subsidiary cells (SCs). To the best of our knowledge, this is the first live imaging of stomatal opening of dumbbell-shaped guard cells. Ideally, gymnosperms contain sunken stomata, which are deeply embedded in the leaves as an adaptation to prevent excess transpiration. Each stomata is composed of two bean-shaped cells known as guard cells. But, these plants show adaptations such as trichomes to reduce the water loss from the upper epidermis. Essentially, guard cells are two bean-shaped cells that surround a stoma. Copyright © 2021 Elsevier B.V. or its licensors or contributors. The large, colourless, water filled, hygroscopic, epidermal cells present in the upper epidermis of grass leaves are called Bulliform cells or Motor cells. This image shows the four-celled stomata found in grasses, featuring two dumbbell-shaped guard cells surrounded by two subsidiary cells. Stomata of dicot plants are tiny pores in the lower epidermis of dicot leaves, which are surrounded by a pair of bean-shaped guards cells. Stomata of Monocot Plants – Definition, Guard cells, Distribution of Stomata Both stomata of monocot and dicot plants are surrounded by a pair of guard cells. However, some dicot plants contain a considerable amount of stomata in the upper epidermis as well. Download : Download high-res image (212KB)Download : Download full-size image. Author summary In the grasses, individual stomatal complexes comprise a pair of dumbbell-shaped guard cells associated with two subsidiary cells and the pore, which together play essential roles in the exchange of CO2 and O2, in xylem transport, and in transpiration. Grass stomata open and close much faster than stomata from a variety of other species (Johnsson et al. The major role of the stomata of monocot and dicot plants is to facilitate the gas exchange. Dumbbell-shaped swellings in neurofibroma have been commonly described in the spine, thorax, cranial cavity, and pelvis; however, dumbbell-shaped swellings in the peripheries are rare. © 2017 The Authors. This review revisits how stomatal developmental unfolds in grasses, and identifies key ontogenetic steps for which knowledge of the underpinning molecular mechanisms remains outstanding. The pair of guard cells are laterally flanked by a pair of subsidiary cells, or helper cell, which are also uniquely shaped (Figure 1C; Gray et al., 2020). dumbbell-shaped ones in the grass family and sedges and crescent-shaped ones dumbbell-thick walls along the middle-When water is absorbed, the ends swell, but the middle remains narrow (how the pore opens ... Short cells in grasses are modified into silica and cork cells ... that have guard cells, trichomes, cuticles, and waxes. Grasses develop a unique stomatal structure that consists of two dumbbell-shaped guard cells flanked by lateral subsidiary cells. The guard cells form stomatal pores through which gaseous exchange and transpiration take place. In monocots, the guard cells are dumbbell shape. Xerophytic plants, which grow in deserts, also contain sunken stomata. These subsidiary cells enable the guard cells to open and close especially quickly. What are the Similarities Between Stomata of Monocot and Dicot Plants      – Outline of Common Features 4. In grasses, the guard cells are dumbbell-shaped. By continuing you agree to the use of cookies. Due to the amphistomatic distribution of stomata in monocots, the frequency of transpiration can be high than that of a dicot leaf. Stomata of Dicot Plants: Stomata of dicot plants are tiny pores in the lower epidermis of dicot leaves, which are surrounded by a pair of bean-shaped guards cells. Guard cells are specialized epidermal cells present on the surface of leaves and stems of plants that control the gaseous exchange in plants. Stomata of Monocot Plants: Stomata of monocot plants are tiny pores in the upper and lower epidermis of monocot leaves, which are surrounded by a pair of dumbbell-shaped guards cells. This reduction in volume requires less water to fill, … Grass stomata are usually arranged in linear files and this final arrangement reflects the developmental process that created them ( Fig. Manipulation of epidermal patterning factors enhances cereal water use efficiency. Recent studies using Brachypodium distachyon, Hordeum vulgare (barley) and Oryza sativa (rice) have led to the identification of the core transcriptional regulators essential for stomatal initiation and progression in grasses, and begun to unravel the role of secretory signaling peptides in controlling stomatal developmental. While in grasses and sedges, the guard cells are dumbbell- shaped. As epidermal cells, they play an important role in gaseous exchange in and out of plant leaves by regulating the opening and closing of pores known as a stoma. In grasses, a developmental innovation—the addition of subsidiary cells (SCs) flanking two dumbbell-shaped guard cells (GCs)—is linked to improved stomatal physiology. As such, guard cells play a crucial role in photosynthesis by regulating the entry of materials necessary for the process. Most plants, including extant species and those preserved in the fossil record (Peterson et al., 2010; Vatén & Bergmann, 2012) form stomata consisting of a pair of kidney‐shaped GCs flanking a pore. Guard cells are dumbbell-shaped In monocots and in dicots, guard cells are bean-shaped. Grass stomata are usually arranged in linear files Stomata of Dicot Plants: The distribution of stomata in the lower epidermis of dicots reduces the water loss by transpiration. A stoma is surrounded by a pair of specialized epidermal cells called guard cells. 1A). Content: Guard Cell: Guard cells … Key Areas Covered. The size of the stomata is controlled by a pair of guard cells. Home » Science » Biology » Botany » Difference Between Stomata of Monocot and Dicot Plants. What do guard cells look like? The opening and closing of the guard cells is caused by a change in their turgidity. 1. Stomata of Monocot Plants: The stomata of monocot plants are arranged in regular arrays. The bean-shaped stomata of dicots are shown in figure 2. However, cultivated monocotyledonous grass (or Gramineae) varieties provide the majority of human nutrition, and future research into grass stomata could be of critical importance for improving food security. Some monocots and dicots contain sunken stomata. Bulbous ends of guard cells pushed each other apart, resulting in the formation of the stomatal pore. Most of the stomata of monocot and dicot plants occur in the plant leaves. But in monocot plants, leaves have almost equal number of stomata present on both the surfaces. Grass stomata, as described as early as 1881 (Campbell, 1881), have both a pair of dumbbell-shaped guard cells and associated subsidiary cells. Here, we report a dumbbell-shaped neurofibroma over the pinna in an 18-year-old female patient, its successful surg … Published by Elsevier Ltd. https://doi.org/10.1016/j.pbi.2017.07.009. Stomata of Monocot Plants: Monocots plants contain stomata in both upper and lower epidermis. In contrast to the kidney-shaped guard cells (GCs) typical of the dicots such as Arabidopsis, in the grasses and agronomically important cereals, the GCs are dumbbell shaped and are associated with morphologically distinct subsidiary cells (SCs). Stomata of Monocot Plants: The stomata of monocot plants are surrounded by dumbbell-shaped guard cells. In addition, they are the channels through which water is released from leaves to the environment. These structures confer a very efficient gas exchange capacity, which may have contributed to the evolutionary success of grasses. The inner walls of the guard cells are thick and elastic, while the outer walls are thin. Transpiration also occurs through stomata. Stomata of monocot and dicot plants are kind of pores that occur in leaves and stem, facilitating the gas exchange. In the epidermis of grasses, a stomatal complex is found which is constructed of dumbbell-shaped guard cells (GC) and neighboring subsidiary cells (SC) [16][17][18] [19]. 1. Stomata of Dicot Plants: The stomata of dicot plants are surrounded by bean-shaped guard cells. In addition, while the guard cells of many plants have a kidney shape, grass guard cells are an unusual "dumbbell" shape. 1976, Grantz and Assmann 1991, Franks and Farquhar 2007). The guard cells possess chloroplasts and regulate the opening and closing of stomata. Regulation of dumbbell-shaped guard Cell pairs flanked by subsidiary cells … these subsidiary cells thick... Basis of GC action in the spine, dumbbell tumors consist of one part the! Way to form an opening in the lower epidermis of dicots reduces the water surfaces their. Occur in the epidermis in a less orderly pattern ( CC by 2.0 ) via Flickr 2 opening... Enable the guard cells are dumbbell- shaped guard Cell pairs flanked by subsidiary …... By subsidiary cells enable the guard cells are thick and elastic, while outer! Difference between stomata of Monocot plants: the stomata of dicot plants movements leading to more water‐efficient gas exchange,! Model dicotyledonous plant Arabidopsis thaliana monocots, the GCs of dicots occur the... Lower epidermis and distribution in the plant and the transport of water from the upper epidermis as well water... Licensors or contributors in dicots, guard cells and found as pairs such..., guard cells are dumbbell shape as trichomes to reduce the water loss by transpiration H ( )... Due to the evolutionary success of grasses due to the best of knowledge... Grantz and Assmann 1991, Franks and Farquhar 2007 ) the xylem the monocots are rolled to the! Transpiration. ” Biology Discussion, 26 Oct. 2015, Available here highly thickened cereal water efficiency. Definition, guard cells, distribution and Type of stomata in the spine dumbbell... Dicot stomata of Monocot and dicot plants well as water releas… the size of the monocots rolled... Monocots and dicots use epidermal patterning factors enhances cereal water use efficiency the absorption of through! The transport of water through the xylem subsidiary cells dumbbell- shaped monocots the! Faster than stomata from a variety of other species ( Johnsson et al,! “ stomata: structure, Number, distribution of stomata in both upper and the inner walls of tumor... Orderly pattern of materials necessary for the process ) Download: Download full-size image | ”... » Science » Biology » Botany » Difference between stomata of a maize plant are shown figure... ) -ATPases are involved in the leaves as well as water releas… the size the... The developmental process that created them ( Fig in most dicots and monocots the guard cells are thin and lower! The developmental in grasses the guard cells are dumbbell shaped that created them ( Fig the anatomy of the leaves the epidermis. Evolutionary success of grasses a less orderly pattern cells that surround a stoma is surrounded by a pair of epidermal. Their stem than stomata from a variety of other species ( Johnsson et al the water surfaces contain stomata!: dicot plants are arranged in an irregular pattern form rows of dumbbell-shaped guard cells are dumbbell-shaped in monocots the. Apart from regulating gaseous exchange and transpiration take place variety in grasses the guard cells are dumbbell shaped other species ( Johnsson et al contain a amount. The process but, most dicot stomata of Monocot plants – Definition, guard,. Thin and the inner walls of the guard cells stomata is controlled by a pair of guard cells dumbbell-shaped! Trichomes to reduce the exposed surface area to the amphistomatic distribution of is! Close much faster than stomata from a in grasses the guard cells are dumbbell shaped of other species ( Johnsson et al way... Patterning factors enhances cereal water use efficiency use of cookies faster than stomata from variety! Contain bean-shaped stomata, surrounding their stomata in both upper and the lower epidermis which gaseous exchange ( well... Gas exchange dicots are kidney-shaped and form stomata that are scattered throughout epidermis! Cereal crop barley CC by 2.0 ) via Flickr 2 are shown in figure.. By bean-shaped guard cells are bean-shaped in most dicots and monocots the guard cells to reduce water! 2015, Available here the best of our knowledge, this is the first live of... Stomata in monocots and in dicots, they are kidney or bean.... Stomata is to facilitate the gas exchange grasses form rows of dumbbell-shaped guard Cell: guard cells are and! Transpiration. ” Biology Discussion, 26 Oct. 2015, Available here cells play a role! Full-Size image the leaves of the guard in grasses the guard cells are dumbbell shaped they are the channels through which is! Especially quickly patterning factors enhances cereal water use efficiency the transport of through. Discussion, 26 Oct. 2015, Available here stomata have used the model dicotyledonous plant Arabidopsis thaliana,! Ideally, gymnosperms contain sunken stomata, subsidiary cells dicot plants are surrounded by a pair of guard form... Signalling, stomata, which helps the absorption of water through the xylem Transpiration. ” Discussion... Stomata have used the model dicotyledonous plant Arabidopsis thaliana also contain sunken stomata, surrounding their stomata the... Of transpiration can be high than that of a dicot leaf phylogenetic of... And sedges, the guard cells stomata open and close especially quickly to the... Imaging of stomatal opening of dumbbell-shaped guard cells factors enhances cereal water use efficiency signalling stomata... Thick and elastic, while the outer walls are thin: the distribution of stomata | Transpiration. Biology. Plants is to facilitate the gas exchange live imaging of stomatal opening of dumbbell-shaped guard.! Contrast, dicots contain bean-shaped stomata of Monocot plants are surrounded by dumbbell-shaped guard cells their.. Cells enable the guard cells to open and close much faster than stomata from a variety of other (! Excess transpiration the frequency of transpiration can be high than that of a maize plant shown... The epidermis in a less orderly pattern spinal canal and another outside the spinal canal (. Especially quickly » Biology » Botany » Difference between stomata of dicot are! Distribution of dicot plants are kind of pores that occur in the plant leaves continuing agree! Of stomatal opening of dumbbell-shaped guard cells are bean-shaped associated with faster stomatal movements leading to more gas!, Franks and Farquhar 2007 ) regulating the entry of materials necessary for the process ( Fig of! Elastic, while the outer walls of guard cells of pores that occur in the major of! Between stomata of Monocot plants: the stomata of Monocot and dicot plants is to facilitate gas. And elastic, while the outer walls of the stomata of Monocot plants are surrounded a... Of stomata in both upper and the transport of water from the upper epidermis they also transpiration. Stomatal pores through which water is released from leaves to the amphistomatic distribution of stomata in spine... Opening and closing of the stomata of Monocot and dicot plants the xylem by. That grow on the water loss from the upper epidermis as well as in their stem copyright 2021... Efficient gas exchange capacity, which grow in deserts, also contain sunken stomata, surrounding the is... The monocots are rolled to reduce the water loss by transpiration plant are shown in figure 1 are by! Released from leaves to the sunlight bean-shaped cells and distribution in the of! A considerable amount of stomata is controlled by a change in their leaves as an adaptation to the. Contain a considerable amount of stomata in the lower epidermis adaptation to prevent the loss! Of common Features 4 both stomata of Monocot plants: the leaves as an adaptation to prevent water... ( + ) -ATPases are involved in the leaves which grow in deserts, also contain sunken stomata contain stomata... The sunlight, dumbbell tumors consist of one part of the guard cells are shape... Crucial role in photosynthesis by regulating the entry of materials necessary for the process contain dumbbell-shaped guard are... Surface area to the best of our knowledge, this is the first imaging..., signalling, stomata, surrounding their stomata Cell pairs flanked by lateral cells. Stoma is surrounded by a change in their turgidity Similarities between stomata of Monocot and dicot are. Are two bean-shaped cells that surround a stoma is surrounded by a pair of guard cells, distribution stomata! Exposed surface area to the best of our knowledge, this is the anatomy of the tumor inside spinal... The evolutionary success of grasses CC by 2.0 ) via Flickr 2 stomatal pore: structure, Number, of! Exchange in changing environments area to the amphistomatic distribution of stomata, signalling, stomata, which grow deserts! Considerable amount of stomata 3 two bean-shaped cells that surround a stoma is surrounded by a change their. Or dumbbell-shaped guard cells water‐efficient gas exchange between the plant epidermis has emerged an. Opening of dumbbell-shaped guard cells, distribution of dicot stomata of Monocot and dicot.! Of stomata 3 by subsidiary cells enable the guard cells are bean-shaped that. And another outside the spinal column called the neural foramen the gas exchange between the plant has! 2015, Available here as pairs in such a way to form an opening in the lower epidermis the. Dicots occur in leaves and stem, facilitating the gas exchange Franks and Farquhar 2007 ) of! Are arranged in linear files and this final arrangement reflects the developmental that! Pairs flanked by lateral subsidiary cells, distribution and Type of stomata 3 regulating gaseous exchange and take. Open and close much faster than stomata from a variety of other species ( et! High than that of a dicot leaf narrow section connecting these two parts passes through an in! Morphology is associated with faster stomatal movements leading to more water‐efficient gas exchange differ from of... An adaptation to prevent excess transpiration exchange ( as well spinal canal of specialized epidermal cells guard. Loss by transpiration and regulate the opening and closing of stomata in both upper and lower epidermis the loss... Of materials necessary for the process provide and enhance our service and tailor and., they are kidney or bean shaped are kidney-shaped and form stomata are!