Anatomy and Histology. 127 



drought, as, presumably, final resultants of a complete antithesis of soil- 

 water conditions. In these one observes a thinner leaf, though slightly 

 more strongly cutinized, in the field plant (plate 35, fig. 13), otherwise but 

 little difference is to be seen. In both the structure is strongly isolateral, 

 with six layers of cells in each, but one may detect a somewhat more exten- 

 sive system of intercellular spaces in the irrigated plant (plate 35, fig. 15), 

 though it must be said that the difference appears but slight. The canals 

 show no appreciable difference. Neither the stomata nor the substoma- 

 tal spaces afford any ground for special comment, while the outer epider- 

 mal walls are, contrary to expectation, slightly thicker in irrigated plants. 

 A denser trichome covering in the field plant may indeed compensate for 

 this, but the observed differences are very slight. 



It remains possible that differences in the character of the soil in 

 which these plants grew are responsible for the close similarity, but the 

 rate of growth in the irrigated plants and their resulting general mesophy- 

 tic character minimize the value of the supposition. 



