Anatomy of or.wrLE. 175 



the culture of the plant, and these have shown that after 

 many failures the plant may be reproduced (in cultivation?) 

 both by seeds and by cuttings. Ross does not mention the 

 kind of cuttings. iMy experience has failed to producel 

 growing cuttings sa\'e of one kind, and it would be interest- 

 ing to know if Dr. Ross' experience has been the same. 



St'cfi'tiofi of rubber and xiciter. The problem of the 

 relation of irrigation to rubber secretion is raised by Dr. 

 Ross, who observes that, while with increase of water 

 the plant grows more rapidly, the matter of secretion under 

 similar circumstances has not been investigated. It is ob- 

 served that experiments are in progress, in the meantime, in 

 certain German colonies in S. W. Africa, which country 

 offers prospects for the culture of guayule. Later in the 

 paper the important fact is pointed out that the rubber is 

 secreted, not as in the commoner rul)ber plants of cultivation, 

 such asCdstillod, in tubes (latex tubes), but occurs in nearly 

 all the cells of the ground tissue: in the pith, medullary 

 rays and cortex, which tissues in winter are densely filled 

 with the material. The leaves have very little, and the 

 wood none. Ross is the first to point out this fact, a very 

 important one physiologically as well as economically, for 

 this it is which favors a mechanical process of extraction. 



7 he facts are now at hand to enable us to gi\e a clear 

 If not strictly quantitative statement of the relation of rubber 

 secretion in guayule to water supply, or, as it would better 

 be put, to rate of growth, as this appears to be the more 

 fundamental relation. If we examine the tissues of field 

 plants in the period of rapid growth following rainfall in 

 the summer, we shall find a clue to the question which Dr. 

 Ross indicates. In a newly grown stem of sav ^ cm. 

 length, taken before induration of the tissues has set in, no 

 rubber will be found at all except very near the base. In 

 about two months we may note the first appearance of rubber 

 in the pith cells, within about kj mm. of the base. At 6 

 mm., 4 mm. further down, a similar small amount, appear- 



