CHARACTERS IN THE LEAF. 31 



forms of Festuca, but the degree of con- 

 stancy or value of each character must first 

 be determined." 



By experimenting he claims to have found 

 a solid foundation for the estimation of these 

 characters. 



He finds the mesophyll and fibre-vascular 

 bundles quite uniform with all sorts of treat- 

 ment of the plants, but the epidermis offers 

 remarkable differences, especially that on the 

 lower side of the leaf. This difference is ap- 

 parent in the thickness of the outer walls, the 

 size of the cavities, and the existence or ab- 

 sence of projections on the partition walls. 

 The dry, cultivated plants had their epider- 

 mis strongly thickened toward the outside, 

 the cavities diminished, and over the partition 

 wall had developed cuticular projections. 

 The moist cultivated plants produced slightly 

 thickened epidermis cells, broad cavities, and 

 no trace of cuticular projections. 



The sclerenchyma or bast, or hypodermal 

 fibers, varies much with different soils and 

 amount of moisture. Species of moist, shady 

 habitats, show in their leaves a clear prepon- 

 derance of the assimilating over the mechani- 

 cal system. 



In very many respects, it will be seen, that 

 a critical study and close comparison of the 



leaves of grasses will reveal a wonderful vari- 



,, . , ., , FiG. 50. Young blade 



ety m their structure and cannot fail to of Trtticum vulgar e 



(wheat) twisting with the 



excite the admiration of every student. In 



certain portions of the preceding account of the leaf, the writer 



has followed Duval-Jouve. 



