Anatomy and Histology. 



119 



same in all, though its irregularity makes accurate measurement impos- 

 sible. When dry it is thickest in the Cedros field plant, thinnest in the 

 Chihuahuan plant, and intermediate (though much more irregular in 

 thickness) in the Cedros irrigated plant. The differences in the cortex are 



Table 44. Comparative radial measurements, in millimeters, of medium-sized stems 

 of guayule, wet and dry. Wood {dry) cylinder 20 mm. diam. in all. August 

 29, 1909 (fig. 16). 



The irregularity in the thickness of the cork makes it difficult to measure it 

 properly. It is, at all events, less than 1 mm., and relatively thinner in field plants. 



apparent ; the index of imbibition of the wood cylinder, while still greater 

 in the Cedros field plants, is relatively much smaller than in smaller stems, 

 because of the compression of the medullary rays. 



Tables 45 and 46 are based upon comparative measurements of Cedros 

 field and irrigated plants. The latter material, however, was collected in 



Table 45. Relative amount of bark and wood in guayule, by volume {dry). Irrigated 



plants (Cedros, Apr. 1909). 



Nos. 1 to 10, stems from single plant taken Apr. 1909. No. 11, stem from 

 different plant taken Sept. 1908. This is the trunk (main) brought from Saltillo. 

 No. 12, root from plant taken Sept. 1908. No. 8, base of piece through crowded 

 nodes, bottom of 1909 growth, hence bark a little thicker here. 



April 1 909. At this time growth had only just recommenced, from which it 

 is evident that the amount of water received between September 1908 

 (at which time I left Cedros) and the time of my later visit was very 

 small and the information obtained showed this to have been the case. 

 The chief value of these tables, besides indicating somewhat more 

 fully the points already made, lies in the evidence they bear that the ratio 



