8o8 
Compton. — An Anatomical Study of 
cotyledon takes one of these triads. There is a short cotyledonary tube 
(Fig. 24). The two main plumular traces appear in the intercotyledonary 
plane. Thus the transition is of a normal intermediate type, as might be 
expected in a seedling of this diameter 1 . 
The transition has also been described by Gerard, 2 with whose descrip- 
tion my own observations agree, except that he says that £ the vascular 
bundles of the root do not meet in the centre \ 
Schizocotyls. Numerous examples were seen in which one or both 
of the cotyledons were more or less deeply bifid. In some cases there 
was a slight notch of 1 or 2 mm., in others the half-cotyledons were only 
united by a few millimetres at the base : and intermediate degrees of 
fission were abundant. 
Hemitricotyl A. Fig. 25 shows the degree of lobing of the one bifid 
cotyledon and the venation of the two seed-leaves. Diarchy persisted till 
after the two root-xylems had separated. Just above the collet one of the 
protoxylems divided radially and equally, and the distance between the two 
halves gradually widened : the position at 5 mm. above the collet being 
shown in Fig. 26. A little higher up a new group of phloem appeared in 
the segment between the two half-protoxylems, these separating still 
further, the result being the formation of a middle collateral strand lying 
between the two half-protoxylems (Fig. 27, at half-way up the hypocotyl). 
This middle strand then divides radially, and so three triads are organized 
(Fig. 28) ; the two arising from one pole of the root entered the bifid seed- 
leaf, the third entering the entire one. The plumular vascular strands were 
two in number as in the dicotyl, and lay in the corresponding plane ; two 
primordial leaves were present at the first epicotyledonary node. 
Hemitricotyl B. The abnormal seed-leaf was divided nearly to the 
base. The chief difference from Hemitricotyl A was that the second pole 
of the diarch root divided radially 5 mm. below the collet ; i. e. below where 
the transverse division of the two xylems took place (Fig. 29). Corre- 
sponding with this, the separation of the two triads serving the split 
cotyledon took place lower down in the hypocotyl. 
Hemitetracotyl C. Two cotyledons were present, each being divided to 
about the same extent as the single split one of Hemitricotyl A, and the 
transition was essentially similar in all three cases; the main difference being 
that the division of the protoxylems was deferred to a much higher level, to 
three-quarters up the hypocotyl on one side and to the base of the seed-leaf 
on the other. Similar instances of slight lack of parallelism between the 
division of cotyledons and vascular system were frequently observed in 
other cases. 
Tricotyl D. The three cotyledons were not exactly equal, one being 
distinctly larger than the other two. This is a general feature of terato- 
1 Compton (’12), pp. 67, 96. 2 Gerard (’81), p. 396. 
