56 COLLEGE BOTANY 



food produots. These .functions of support and transportation 

 are performed by the stem. 



The secondary functions are: (1) photosynthesis by green 

 st.ems in the same manner as the leaves (page 195). This is of 

 secondary importance in most plants, but is a primary function 

 in such plants as the cactus, in which the leaves are of no con- 

 sequence. (2) For the storage of water and reserve foods, as in 

 the case of the cactus, the tuber of the potato and the fleshy 

 biilbs. (3) For climbing, as in the case of the morning-glory, 



Fig. 33. — Ivy holdfast type of stem. Fig. 34. — Thorn type of stem.- 



the grape and some of the ivies (Figs. 32 and 33). (4) As 

 thorns (Fig. 34), in the case of the honey locust and hawtho'm. 

 (5) For reproduction, as in the case of many underground stems, 

 the willows, grapes and many other plants. The tendency ot 

 many plants to reproduce by means of stems is utilized by the 

 growers. The tubers, or underground st^ms of potatoes, are 

 always used in the growing of this crop. Grape-s, roses, ger- 

 aniums, begonias, carnation, privet, willows and a whole 

 host of other plants are very generally p'ropagated by means 

 of cuttings. Bulbs are also used for the growing of many 

 plants. The stems are also used in grafting and bud- 

 ding (page 103). 



