IV] HETEROPHYLLY 71 



tions of grass leaves. The results, which are based on the 

 elaborate investigations of Duval Jouve, Schroeter, Pde- 

 Laby and Grob, as well as on my own observations, are 



Fig. 28. Transverse section of subulate leaf of Aira fiexuosa ( x about 

 50), the upper surface represented by a mere ridge with two flanking 

 grooves each with but traces of motor-cells below. One large 

 vascular bundle and four much smaller ones are seen. There are no 

 girders, but slender bands of solerenchyma at the lower surface 

 nearly join into a continuous sub-epidermal sheath. This type is 

 the extreme form of that in Fig. 26. 



not complete in all respects, and much more should be 

 done to extend the theme, but the account given will 

 serve to show the student how such results may be 

 employed. It is as yet impossible to decide how far these 

 characters are constant — they are known to be fairly so in 

 many cases — but several grasses cannot yet be distin- 

 guished by them alone. 



It should also be added that some grasses develope 

 two types of leaves (heterophylly), solid or subulate below, 

 flat or slightly inrolled above — e.g. Festuca heterophylla — 

 and the following arrangement is intended to apply to the 

 vegetative lower leaves and not to those on the upper 

 parts of the flowering specimen. Moreover the sections 

 should be cut from the basal third of the lamina, and not 

 from the tip of the leaf. 



