— 239 — 



The hairs on the upper surface are comparatively few, but 

 thick and stiff; they are white and eacli one occupies a 

 white circular base. On the lower surface these hairs are 

 very numerous. The white flowers are out in May. 



Heliotropium Radula, so far as it has been possible to 

 determine the frequently sterile light-shoots, seems to have 

 the same mode of growth and the same form of leaf and 

 hair-coating as H. sogdianum. The hair-coating is, however, 

 somewhat closer. 



The leaf of H. sogdianum is isolateral. The epidermis 

 is one-layered, densely hairy (v\dth hair-cystolitlis, see H. 

 dasycarpum p. 222), and with slightlj' sunk stomata on both 

 sides. There are about two layers of short, starch-filled 

 palisade cells on each side. The veins are surrounded by 

 translucent cells. 



Aristida pennata Trin. 



This sand-binding grass has been already dealt with 

 (p. 81—83). The thick, shrubby growth of the plant and its 

 power of forming lateral shoots, which add to the tufts and 

 when buried by the sand form new ones, makes this plant 

 the "Conqueror of the Sand-desert" (Antonow) and the most 

 valuable of all sand-binders. 



It has been already recorded and illustrated (fig. 9) that 

 the roots are encased by a sand - stocking. Within this 

 stocking the root lies loose, "wie das Bein in der Hose oder, 

 besser und asthetischer ausgedriickt, wie eine Phryganeen- 

 larve in dem selbst gebauten Gehause'' (Volkens p. 26). 

 VoLKENS points out that this sand-stocking is formed by the 

 roots -hairs cementing the sand-grains together, and he is of 

 opinion that its function is to protect the roots against 

 evaporation. This is confirmed by the fact that in grasses 

 provided with a sand-stocking, there is no cork or other 

 corresponding means of protection. 



My observations show tliat the root, which sits loose 

 in the sand-stocking, is devoid of cortex. It is enclosed in 

 a thick-walled pericycle consisting of several layers of prosen- 

 chymatous cells with numerous pores and containing starch; 



