332 PRACTICAL BOTANY 



2. The subjacent cortex is thin- walled, and colour- 

 less, and often contains much starch. 



3. The ridges, intercellular cavities of the cortex, 

 and vascular bundles, have the same relative positions 

 as in the aerial stem. 



4. The structure of the vascular bundles is similar to 

 that in the aerial axis. 



5. There is no cavity in the centre of the axis. 



Cut transverse sections of one of the tubers ; treat with potash, 

 and mount in glycerine. Observe 



1. The brown- walled epidermis with many hairs, similar to 

 those on the root-stock. 



2. A sub-epidermal layer with thickened walls. 



3. The bulky parenchyma with numerous starch-grains : there 

 are no large intercellular cavities as in the aerial axis. 



4. Isolated vascular bundles, each of which is surrounded by 

 a special endodermis, quite distinct from that of the other 

 bundles : there is no general endodermis as in the normal 

 axes. 



A comparison of the stems of various species of Equisetum in 

 respect of the endodermis shows that there is some want of 

 uniformity in its arrangement, even in the normal axes : further, 

 it has been shown that such differences may occur between the 

 rhizome and the aerial axis even in the same species. In E. 

 arvense there is a difference in this respect between the tubers 

 and other axes. 



VI. Make preparations suitable for the study of the 

 epidermis in surface view, by cutting longitudinal tan- 

 gential sections, and treat as before, mounting with 

 the outer surface uppermost : observe under a high 

 power 



1. That the superficial cells covering the ridges 

 are of elongated form, with smooth outer walls, and 



