STEMS, BULBS AND BUDS 



53 



(Fig. 28). These structures are developed from the stem sto- 

 niata, which will be described more fully in connection with the 

 structure of the leaf (page 78). 



The stomata are openings into intercellular spaces within the 



FIG. 29. Cross-section showing early stage in the development of a lenticel. 



leaf, stem or other part of the plant and permit of the free access 

 of air into the interior. The cells just beneath the stomata of 

 the stem increase in number, become corky and finally rupture 



FIG. 30. Cross-section showing late stage in the development of a lenticel. 



the epidermis (Figs. 29 and 30). They continue to permit the 

 free access of air to the interior of the stem but prevent the 

 passage of water. These lenticels are very easily recognized 

 as small specks on young woody stems and sometimes are very 

 prominent on the older stems, especially the birch trees. 



