116 



Guayule. 



THE EFFECT OF ABUNDANT WATER UPON ANATOMICAL 

 STRUCTURE. 1 



The effect of irrigation upon the structure of the mature plant is very 

 marked. This is especially noticeable with respect to the relative volumes 

 of the wood cylinder (including pith and medullary rays) and the " bark ' ' 

 (cortex and cork) . As this is a question of prime importance economic- 

 ally, it will be treated first. 



By means of weighing, Whittelsey (1909) determined that, in vari- 

 ous portions of the plant, the trunks are made up of 44 to 65 per cent bark 

 (cortex and cork) , the amount of bark being relatively larger in the smaller 

 twigs. The material was quite dry. (Table 40, page 115.) 



In Whittelsey 's determinations , the pieces examined were first steamed 

 to render it possible to separate the wood from the cortex. A slight 



Fio. 16. Relative dimensions of wood cylinder and cortex, wet and dry.'in twigs of field and 

 irrigated plants. X 20. 



error is introduced by this method, as some of the resin exudes from the 

 cut ends of the cortex and infiltrates into the wood. This error is appar- 

 ent in table 41 , in which the ratios of steamed material are smaller than in 



TABLE 41. Ratio of bark to wood by weight for field and irrigated shrub, as deter- 

 mined after (a) steaming, (b) moist chamber. 



Two pieces each of field and irrigated plants (Cedros, April 1909): (a) Field 

 plant pieces 3.9 to 4.8 mm. diameter; (b) irrigated plant pieces, 3.4 to 4 mm. diam- 

 eter. Each piece of (a) segmented into fourths and alternate fourths placed in 

 each of two lots; (b) segmented into fourteenths, similarly placed in each of two 

 lots. One lot (I) of (a) and of (6) steamed, de-barked, dried in oven, and weighed. 

 The other lot (II) of each placed in a moist chamber till fit for separating wood and 

 bark; then dried in oven and weighed. 



1 The substance of what follows under this caption was presented in a paper 

 entitled "The Responses of the Guayule, Parthenium argentatum Gray, to Irriga- 

 tion," before the Botanical Society of America, at its Boston meeting, December 

 1909. (Lloyd, 19106.) 



