Closed Style - Style of Stigma Interaction
Cotton shows an epidermis with stomata, a cortex of thin-walled parenchyma with several vascular bundles and strands of transmitting tissue. The cells of transmitting tissue have thin transverse walls but lateral walls are thick and consist of several distinct and concentric layers. The innermost wall layer 1, is composed of pectic substances and hemicellulose, surrounding this is wall layer 2 which is darker, thinner and similar to wall layer 1 -in composition with a large hemicellulose content. Wall layer 3 is loosely textured rich in pectin substances and contains small amounts of noncellulosic polysaccharides and cellulose but poor in hemicellulose. Wall layer 4 is represented by the middle lamella region and is primarily pectic in nature.
Small amounts of protein is also present in layers 3.4 (3 also contains masses of small vesicles). The cells of transmitting tissue contain many mitochondria and active vesicles forming dictyosomes. The plastids are large with numerous amyloplasts, polysomes and abundant rough ER. Transmitting tissue cells have a spherical or slightly ellipsoidal vacuole. Nuclei are large and frequently lobed indicating their active metabolic state. EM studies of transmitting tissue in Petunia, Lycopersicon and Nicotiana and some other taxa show that the cells in general have thin walls traversed with plasmodesmata.