207 
Vascular System of the Genus Equisetum. 
of the node above and are situated on the same orthostiches. Examination 
of cleared preparations shows that the first element to differentiate in each 
strand is a tracheide which often extends through the whole length of the 
internode, or there may be two tracheides joined end to end. Further 
differentiation results in the addition of other tracheides in a more peripheral 
position. 
The traces in the leaves develop concurrently, the tracheides first 
differentiating in the distal region, but very soon linking up with the proto- 
xylem of the internode, either directly or by the intervention of one or two 
Text-fig. 2. Longitudinal section of basal region of primary axis, showing an early stage in 
the development of the first lateral bud. Note abortive leaf-trace adjoining foot. 
Text-fig. 3. Diagram illustrating the apex of a sporeling, showing the independent 
development of the internodal xylem strands of successive internodes. The nodal tracheides have not 
yet differentiated. 
Text-fig. 4. Diagram of apex of older shoot illustrating the xylem development prior to the 
differentiation of the metaxylem. The nodal tracheides already link up the successive internodal 
strands. 
nation of the leaves of successive segments, which is so characteristic 
f a feature of Equisetum , necessitates the development of a connecting system 
at the nodes. In the youngest nodes no such linking up is at first apparent, but 
provision is soon made for a continuous conducting system by the special- 
ization of certain of the parenchymatous cells of the nodes (Plate VII, 
Figs. 3, 4). These cells develop into short obliquely placed reticulate tracheides, 
so arranged as to connect up the strands of successive internodes (Text-fig. 4, 
and PL VI, Fig. 7). This nodal structure is a most characteristic feature of 
P 
