Vascular System of the Genus Equisetum . 225 
the structure of these bundles and that of the bundles of the vegetative stems 
will be discussed below. 
Although, as already stated, the protoxylem strands determine the 
main features of the vascular system, yet the very considerable development 
Text-fig. 22. Diagram illustrating the vascular system of the cone of E. arvense. The 
metaxylem is represented by shaded area and the protoxylem by continuous lines. The black circles 
enclosing central dots represent the point of attachment of the sporangiophore traces. 
Text-fig. 22#. Part of the vascular system of a cone of E. arvense , showing more extensive 
tracts of metaxylem. 
of metaxylem in the bundles may tend to obscure the course of the 
primary strands (Text-figs. 22 and 22 a). Moreover, the metaxylem may be 
unequally developed on either side of a protoxylem strand, and may in 
certain regions be so well developed as to form lateral connexions with 
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