In the first place, it bears leaves , and is divided into nodes and internodes. The consequences of this are that not only is the form of the stem apex modified, but the development of the stem apex is intimately bound up with the formation of leaf primordia. Moreover, because of the presence of a branching vascular supply to the leaves, the internal structure at the node is much more complicated than at the internode. The cortex of the stem usually contains more tissue types than the corresponding region in the root, a feature that may be related to the aerial habit of the stem, as well as its mechanical function. Thus, we may find stomata in the epidermis and chloroplasts in the cortical parenchyma.
Mechanical tissue is usually abundant, in the form of collenchyma and sclerenchyma.
In addition, there is a great variation in the detailed structure of stems of different species. Examine the water mount and note that the thickened primary walls show up clearly. Inner cortex - consists of parenchyma, containing numerous chloroplasts. This zone varies considerably in width, but does not usually extend round the corners of the stem. Endodermis . , or starch sheath - a single layer of rather large cells, forming the inner limit of the cortex.