215 
Vascular System of the Genus Equisetum . 
chyma, is a complete absence of air-channels in the tuber. In the tubers of 
the sporelings there are usually four bundles embedded in a great mass of 
starch-containing parenchyma. Each vascular strand is surrounded by 
a very evident endodermis, and in this respect the tuber of E. arvense 
differs from any of the other shoots of this species (Text-fig. 9). 
Tubers which are formed on the rhizomes of mature plants vary con- 
siderably in form, as has been fully described by Duval-Jouve (12) and 
Milde (13). They may consist of single swollen internodes, or of a series 
similar to the well-known case of Arrhenatherum avenaceum . 
I11 the more swollen tubers, as Leclerc du Sablon (14) has shown, the 
vascular strands branch before reaching the greatest diameter and link up 
Text-fig. 10. Diagram of transverse sections of abnormal tuber. A. Close below a node. 
B. Middle of the internode. 
again before passing through the nodal region. The same author has 
pointed out that each vascular bundle is made up of mixed tracheides and 
parenchyma, and the xylem does not show a separation into three parallel 
strands. 
Among the material examined during the present investigation one 
tuber of E. arvense was met with which exhibited a distinctly anomalous 
structure. It was noticed that in transverse section the bundles appeared 
to be much elongated in the radial direction, and on closer inspection it was 
found that the protoxylem, consisting of one or two extremely narrow 
elements, was separated from the remaining xylem by a group of parenchy- 
matous cells, the endodermis encircling the whole bundle (Text-figs. 10 (a, b), 
11, and 12). A series of sections was taken through the remainder of the 
internode, and from this it was seen that towards the widest region of the 
