Holden. — Observations on the 
326 
necessary gap (Figs. 26, 27, 28). A transverse section of the epicotyl at 
this point will therefore, if no prior lateral fusions have occurred, reveal 
a system of twenty-two bundles comprised as follows : 
(a) Two sets of three from the lower pair of leaves ; 
(b) Two sets of three from the upper pair of leaves ; 
(c) Two sets of three from two of the leaves of the lower whorl ; 
{d) Four bundles from the remaining leaf of the lower whorl ; 
namely, the laterals and bifurcated midrib (Fig. 27), this number being 
reduced to fourteen by the lateral fusions to which reference has already 
been made. A further reduction to 
twelve bundles is next produced by the 
fusion of each of the two undivided 
median bundles from the lower whorl 
with one of the laterals of the adjacent 
leaf of the basal pair (Fig. 28). The 
twelve bundles are reduced to six by 
the unequal fusion of those of the 
upper pair of leaves with those of the 
lower pair, the median bundle and one 
of its laterals fusing with one set of 
lower pair laterals, whilst the remaining 
laterals of the upper pair fuse with 
the other set of lower pair laterals. 
A certain compensatory principle is 
observable in this unequal fusion, the 
two pairs of bundles fusing with the 
laterals which received the products 
of the bifurcating strand, whilst the 
remaining bundle fuses with the laterals 
which received two bundles each at 
the previous node. The six bundles 
so formed enter the apex of the hypo- 
cotyl in the intercotyledonary plane 
and eventually fuse to form two xylem 
masses which, in fairly old seedlings, are continuous with a patch of 
secondary xylem immediately below them. The relationship of the 
epicotyledonary strands to the vascular strands of the cotyledons is also 
a feature of some interest, especially in mature seedlings. 1 As the latter 
approach the former they appear in transverse section as bow-shaped 
systems, the ends of which extend beyond the laterals from the epicotyl. 
At the same time connexion is established between the two by the phloem 
1 By mature seedlings is meant those in which vigorous epicotyledonary growth has begun and 
in which the cotyledons have attained their full development. 
Fig. 28. Diagram indicating the course 
of the bundles in the young epicotyl. 
