DALBEY: SOME SPECIES OF XANTHIUM. 59 



1 to 1, and in X. globosum and X. americanum 1 to 1.6. In 

 X. pennsylranicum the palisade cells of one section varied in 

 length from .033 mm. to .062 mm. (figs. 5 and 6) . In the other 

 species this variation was not so great, being .030 mm. to .037 

 mm. in X. globosum (fig. 7), and .030 mm. to .045 mm. in 

 X. americanum (fig. 8). 



In cross sections of the leaves of the different species, which 

 had been treated with alcannin, the mesophyll cells contained 

 large bodies which stained a bright red. When the sections 

 were put into ether and then treated with alcannin the same 

 bright-red bodies were seen, but when treated to boiling in 

 Fehling's solution, and left in the solution several hours at a 

 temperature of about 35° C, copper oxide crystals replaced 

 these round bodies. Since the reaction for sugar did not oc- 

 cur except after long contact with Fehling's solution, the bodies 

 are probably glucosides, which yield sugar after hydrolysis 

 by long standing in Fehling's solution. 



The cells of the epidermis are rather irregular in size (fig. 

 4, /). In cross section the average diameter parallel with the 

 circumference is in X. pemisylvanicum .015 mm., in X. amer- 

 canum .0131 mm., and in X. globosum .0135 mm. In tangential 

 section the epidermal cells of X. pennsylvanicum are more ir- 

 regular in shape than the epidermal cells in the other species 

 (figs. 16, 17, 19). 



A ridged cuticle layer covers the outer cell walls in each 

 species. 



Stomata of the usual type (figs. 14, M; 16, O) occur on both 

 sides of the leaf, more numerous in X americanum than in the 

 other species, as the following tabulation will show : 



Upper side. Under side. 



A', pennsylvanicum .... 243.5 to sq. mm. 205.8 to sq. mm. 



X. americanum 309.9 to sq. mm. 270.5 to sq. mm. 



X. globosum 196.0 to sq. mm. 166.0 to sq. mm. 



In cross section the guard cells are much smaller than the 

 adjacent epidermal cells, as the following comparison shows : 



Guard cells. Adjacent epidermal cells. 



X. pennsylvanicum 005 mm. diam. -.017 mm. diam. 



X. americanum 007 mm. diam. .030 mm. diam. 



X. globosum 005 mm. diam. .020 mm. diam. 



Numerous trichomes of two different forms occur on both 

 surfaces of the leaf (fig. 22, E and F) . 



The most conspicuous one is a large hair with an average 

 length of .14 mm., composed of a basal cell, one or sometimes 



