Seedling Structure of Gymnosperms . ///. 439 
smaller five, [some of which fused together so that four entered the axis from 
each seed-leaf. 
These observations are in agreement with those of Worsdell, 1 who has 
briefly investigated the seedling of this plant and draws attention to the 
similarity of M. spiralis and Cycas in the structure of the cotyledons. 
Transition. 
Taking the commoner occurrence, as regards the number of cotyle- 
donary traces, nine vascular bundles enter the hypocotyledonary axis and 
travel towards the centre with some degree of rapidity, so that, in trans- 
verse sections, the traces are always very oblique, which renders it almost 
impossible to distinguish the protoxylem elements from the metaxylem, 
for which reason the protoxylem has not been indicated in all the figures of 
the second and succeeding Diagrams. During the passage various fusions 
take place between adjacent bundles ; thus, to take a concrete case which is 
illustrated in Diagram 2, i joins up with a (Diagram 2, Fig. 1) ; c and d , 
as they pass inwards, approach each other and fuse (Diagram 2, Figs. 2 and 
3) ; and likewise the bundles /and^. At a slightly lower level b joins with 
the compound bundle cd and, similarly, h fuses with fg. So far e has 
remained isolated, but it very soon effects a junction with by which time 
the xylem-masses of the cotyledonary strands have fused with what wood 
is present belonging to the plumular traces. There is thus formed a very 
irregular core of xylem, which, sometimes, is roughly three-rayed, in the 
centre of the axis. The phloem-masses also fuse so that the vascular tissue 
derived from the cotyledons and from the plumule forms a single concentric 
cylinder (Diagram 2, Fig. 6). This condition obtains only through a very 
short length of the axis ; the phloem separates into two masses situated in 
the intercotyledonary plane and, concurrently, the xylem elements, which 
by now are rather less numerous than before, become organized to form 
a well-marked diarch plate situated in the cotyledonary plane. 
In no case has a transient tetrarch root-structure been observed, and, 
so far as has been seen, it is generally diarch, an observation which is 
in agreement with Worsdell’s 2 experience. During these later changes, as 
has already been remarked, it is impossible to trace the protoxylem or to 
distinguish it from the metaxylem owing to the numerous and complicated 
anastomoses. It is therefore impossible to say whether or not all the 
cotyledon-traces are equally important in the formation of the resulting 
root-structure. It is obvious, from the strongly mesarch nature of the 
cotyledonary bundles, that the rotation of the protoxylem is of very little 
importance for the amount of centrifugal wood is so small that only a slight 
1 Worsdell : The Comparative Anatomy of certain Genera of the Cycadaceae (Journ. Linn. 
Soc. Lond., Bot., xxxiii). 
2 loc. cit. 
