Seedling Structure of Gy mno sperms. Ill . 453 
the same kind of variations obtain in this plant as we have shown to occur 
in others. As regards morphology, the material at his disposal contained 
one seedling with two cotyledons naturally developed, of these one was 
slightly larger than the other, and each had in the upper regions ten or 
twelve vascular bundles, which by fusion became reduced to three in the 
basal parts. There is no cotyledonary tube such as obtains in Enceph- 
alartos Altensteinii. The cotyledonary strands enter the axis and fuse on to 
the plumular traces, thus forming an elliptical concentric vascular cylinder 
from which a diarch root-structure is organized, the two poles being in the 
plane of the cotyledons. At a lower level a third pole is differentiated. 
In another example having but one cotyledon eight vascular strands 
entered the axis, fused in pairs, and gave rise to a triarch root-structure. 
Ceratozamia longifolia $ x C. mexicana a 71 - The seedlings of this 
hybrid have been described by Van Tieghem , 1 who does not enter at all 
fully into the transition-phenomena. Monocotyledony appears to be the 
rule, but one out of four examples examined seemingly had two cotyledons 
of very unequal size ; Van Tieghem concludes that this specimen was really 
monocotyledonous, and the apparent smaller second seed-leaf was nothing 
more than a lobe of the larger one. The cotyledons generally have eight 
vascular strands which fuse in pairs as they are traced downwards, so that 
four traces enter the axis and give rise either to a triarch or a tetrarch root. 
The apparent dicotyledonous specimen had six seed-leaf bundles and the 
root-structure was triarch. 
Microcycas. 
Microcycas calocoma. The germination and structure of this plant has 
been described by Miss Dorety . 2 The cotyledons are two in number, and 
for the greater part of their length are fused very closely together by their 
ventral surfaces ; basally they form a tube. Each seed-leaf has in its 
upper region eight to ten vascular bundles, all of which are derived from the 
branching of three. The transition is of the same type as that occurring 
in Dioon edule y as described by Matte and Thiessen. The corresponding 
lateral bundles of each cotyledon fuse together, thus four strands obtain. 
‘ The metaxylem and phloem divide, as usual, and the resulting portions 
swing to right and left, the right half of the phloem of each joining with the 
left half of that of the next, with sometimes the lowermost extremities of 
leaf-trace phloem intervening. There is thus produced the characteristic 
root-structure, four groups of phloem alternating with four double-fan-shaped 
xylem groups.’ In some cases the tetrarch arrangement became reduced to 
triarch towards the apex. 
1 Van Tieghem : Symetrie de la structure des plantes (Ann. Sci. Nat., Bot., xiii, 1873). 
2 Dorety : Vascular Anatomy of the Seedling of Microcycas calocoma (Bot. Gaz.,xlvii, 1909). 
