194 



STEMS 



71). This milky juice is called latex. It is an accumula- 

 tion in which water, food, and waste products are all pres- 

 ent. Its function is not well understood. It is usually 

 contained in tubes which result from the fusion of many 

 cells, or, as in the milkweed, result from the growth of 

 special cells which, as they grow, crowd their way through 

 the softer cells of the cortex. The latex vessels run through 

 the entire plant somewhat as the vascular tissues do. 

 (See Figure 6y.) A familiar example of latex, besides that 



of the milkweed, is the 

 reddish juice of the 

 bloodroot. Members of 

 the spurge family are 

 common plants all of 

 which have abundant 

 milky latex. 



Latex is of much eco- 

 nomic importance for 

 the reason that it con- 

 tains caoutchouc (kou'- 

 chook), the substance 

 from which rubber 

 is made. Although 



Fig. 67. — Tissue of the wild lettuce showing more Or less of Caout- 

 the way in which the latex tubes («) branch cn0U C see mS to be preS- 

 among the other cells. 



ent in all latex, that of 

 only a few plants has been found profitable to use in the 

 manufacture of rubber. Certain trees, either native to 

 South America or thriving there under cultivation, produce 

 the world's principal supply of caoutchouc. Other tropical 

 trees, similar to these rubber trees, produce a latex from 

 which gutta-percha is derived. Besides its use for golf 



