founded on the Structure of their Seedlings. 49 
cotyledonary traces into the root-stele. They are always 
accompanied by two or three plumular traces, and they enter 
the stele from opposite sides. Thus the two groups of 
cotyledonary elements in the xylem of the root-stele are 
separated from each other by two or more groups of plumular 
elements. The root is often tetrarch or pentarch : sometimes 
hexarch or heptarch. The details of transition are never 
quite clear, but the process follows Van Tieghem’s type 1. 
In Desmoncus sp. the root, which is tetrarch when first formed, 
becomes octarch lower down. 
The habit of the seedling of Phoenix dactylifera is very 
distinct from that of any of the Palm seedlings just de- 
scribed. The bundles of the inflated cotyledonary sheath 
form a circle of about ten, which are all continued into the 
primary root. The plumular traces are of course internal to 
this circle from the beginning. They are inserted on the 
cotyledonary traces without affecting the symmetry of the 
primary root-stele. The transition to a root-structure takes 
place by the branching of the xylem (Van Tieghem’s type 1), 
and the root is commonly 10-arch. 
The absence of a midrib in the cotyledon of the Palms 
is conspicuous not only in all the seedlings described, but also 
in two others which I have partly examined, Geonoma oxycarpa 
and Chamaerops humilis . But it should be added that the 
foliage leaves do not always possess a midrib, and that when 
present it is little distinguished from the others. 
The adaptations to an arborescent habit are so well marked 
in all the species that the presumption is certainly against the 
primitive character of any particular feature. I may, however, 
mention that the well-grown cotyledon of Chamaerops humilis 
when extracted from the seed is seen to have a bifid apex. 
I remarked on this in my notes before the theory of a com- 
pound cotyledon had occurred to me, and compared it to the 
two lobes of a brain. The cotyledon of Ch. Fortnnei is still 
more completely bilobed. This may very possibly be an 
adaptive character, but I should be glad to know whether 
it occurs generally among large-seeded Palms. 
E 
