233 
Vascular System of the Germs Equisetum . 
4. The vascular^structure of an anomalous tuber is described, in which 
carinal canals are formed in connexion with the protoxylem, and these in the 
middle region of the tuber are enveloped by separate endodermes. 
5. A young sporeling of E . lirnosum is described showing a forked* 
primary axis. The arrangement of the vascular system indicates that it has 
almost certainly arisen by a dichotomy. 
6. The question of the existence of secondary thickening at the nodes 
of E. arvense and E. maximum has been investigated by a study of the 
development of the nodal tracheides. The conclusion is formed that the 
apparent increase in elements which has been attributed to secondary 
thickening" is due to the enlargement and displacement of developing 
tracheides. 
7. The vascular structure of the cones of E. arvense , E. maximum , 
E. palustre , E. lirnosum , and E. sylvaticum is described. 
The endogenous protoxylem strands are shown to form complete and 
continuous systems, uninterrupted by nodal tracheides, as is invariably the 
case in vegetative shoots. The metaxylem develops later and varies in 
amount and distribution in the different species. 
E. ai'vense shows the greatest amount and E. lirnosum and E. sylva- 
ticum the least. 
It is concluded that the gaps in the metaxylem siphonostele cannot be 
described as leaf-gaps, bearing no relation to the sporangiophore traces, but 
may be related to the mechanical efficiency of the cone. 
It is also concluded that the vascular structure of the cone indicates 
that the sporangiophores are not the morphological equivalent of leaves, but 
are organs sui generis, and the axis of the cone is undifferentiated into nodes 
and internodes. 
8. The general vascular system of the plant is discussed, and it is con- 
cluded that the general plan of development proceeds from a simple proto- 
stele which opens out into a siphonostele. This shows a considerable 
reduction in the cone by the development of large parenchymatous meshes 
or longitudinal tracks and still further reduction in the internodes of the 
vegetative shoots. 
In conclusion, the author’s grateful thanks are due to Dr. S. Chandler, 
who very generously handed over some sporeling material and microtome 
sections of Equisetum sp., which he had already prepared. 
Department of Botany, Imperial College of Science 
and Technology. 
