180 APPLIED BIOLOGY 



the stem. Other cells of the stem also play a part in con- 

 duction of liquids, especially in the transverse or horizontal 

 direction. 



(3) Breathing by stems occurs through certain openings in 

 the outside f layers of tissue. The epidermis of herbaceous 

 stems has stomata similar to those of leaves. Examine with 

 microscope epidermis from such plants as bean, tradescantia, 

 and begonia. In plants with corky bark the stomata are 

 replaced by openings known as lenticles (meaning lens-shaped) 

 or stem-pores. Good examples may be seen on young stems 

 of cherry and plum. Notice that on the older parts of these 

 stems the lenticles are elongated by growth. The holes in 

 cork used for bottles look like holes made by worms, but they 

 are lenticles. Examine a bottle cork and note the parallel 

 holes which originally extended through the thick corky bark 

 to the cambium, thus allowing air to penetrate to the active 

 cells. 



170. Special Adaptations of Stems. In addition to the 

 primary functions discussed above, many stems have become 

 adapted or fitted to special kinds of work such as climbing, 

 propagation, living underground, and in still other ways to be 

 described in the paragraphs which follow. 



171. Propagative Branches. Strawberries, red raspber- 

 ries, currant, and gooseberry are examples of numerous 

 kinds of plants which have some branches either lying on 

 the surface of the soil or creeping underground, and which 

 form roots and develop new plants. When these branches are 

 underground, gardeners call the new plants which come up 

 " suckers." 



172. Branches for Climbing : Tendrils. Slender branches, 

 without leaves and buds, are in many plants adapted for 

 climbing. Examine specimens of tendrils from grape-vine, 

 Virginia-creeper, Boston-ivy, cucumber, squash-vines, pas- 

 sion-flower plant, or gourd-plants. Note that some are 

 single tendrils, some are branched, and some have flat 



