Primitive Angiosperms. i6r 
(Tansley and Thomas, 87 ; see also Thomas, 88). If these observations are 
well-founded, the two primitive types ought to resemble each other. If 
they do, the results in either case are strongly confirmed. If they do not, 
there must be some flaw in the reasoning on one side or on both. 
This test has in fact proved satisfactory. The two types of vascular 
structure resemble each other very closely. The points which they have 
in common represent, no doubt, the seedling structure of the Primitive 
Angiosperms. But the important feature for our present purpose is this. 
The seedling structure of the primitive Monocotyledon resembles that of the 
primitive Dicotyledon in its dual symmetry. In other words, judging by its 
vascular skeleton, the seedling of the Primitive Angiosperm was dicotylar. 
The importance of this result renders an examination of the evidence 
on which it is based imperative. The account which follows is necessarily 
a mere sketch. For convenience it begins with the Dicotyledons. The 
external features of their seedlings are more familiar to botanists, a greater 
mass of evidence concerning their internal structure is available, and their 
vascular symmetry is less variable and more easily described. 
The most important series of researches hitherto made on the anatomy 
of Dicotyledonous seedlings from a phylogenetic standpoint is that carried 
out by Mr. A. G. Tansley and Miss Thomas. It is as yet published only 
in abstract. But in the light of their results previous work such as that of 
Gerard (27), Dangeard (20), and others acquires a new value. The seedling 
anatomy of Dicotyledons had been examined much more fully than that 
of Monocotyledons before the microtome came into common use. The 
suppression of the internodes, which is characteristic of Monocotyledonous 
seedlings, was indeed a formidable obstacle to research when the only 
possible method of examination was by successive hand-sections. But 
hand-sections could be used for the fairly long internodes of Dicotyledons. 
Thus Gerard, in his elaborate memoir of 1881 (27), described fifty-seven 
species of Dicotyledons, giving every detail of the transition from root to 
stem in the young seedling, but he attacked only nine species of Mono- 
cotyledons. And as these were necessarily chosen because they possessed 
fairly long hypocotyls and plumular internodes, they did not properly 
represent their class. 
Dangeard gave a more general sketch of the anatomy of Dicotyledonous 
seedlings in 1889 (20), and we have, in addition, accounts of isolated families 
or genera by Van Tieghem, Queva, Sterckx, Chauveaud and others. These 
researches have for the most part been directed to an anatomical end — the 
description of the transition from root to stem-structure in the hypocotyl. 
The evidence then to which I shall refer is, in the first place, that 
collected by Mr. Tansley and Miss Thomas. In the account which follows 
I have drawn largely on both the published abstracts dealing with their work 
