728 Thomas . — Seedling Anatomy of 
Discussion of Results. 
No attempt will be made in this paper to discuss at length the various 
aspects of seedling anatomy, but I shall rather concern myself with 
pointing out the immediate problems suggested by a consideration of the 
forms herein described. 
A review of these species alone would of necessity raise several very 
pertinent questions. 
The universality of the vascular unit of the hypocotyl, which in the 
cotyledonary plane is continued upwards as the 4 double bundle ’ and in the 
intercotyledonary plane as two separate strands, forces itself upon one’s 
attention. 
If the position in the hypocotyl be regarded as an inevitable stage of 
transition from leaf to root, to which view the examination of the strands 
from above downwards predisposes us, we are confronted with the necessity 
of accounting for the difference in behaviour between the central and lateral 
strands. Why do not the lateral strands of the cotyledons behave in the 
same way as the central strand, i. e. each 4 form ’ or relate to a root pole, 
instead of combining with another to do so, and if root structure is ‘ carried 
up ’ in the central bundle, why not in the lateral strands also ? 
If with Chauveaud we regard the root as of paramount importance, to 
which I cannot but think the examination from root upwards inclines us, 
we tend to become overpowered by conceptions gained from a consideration 
of root structure, and while these offer a very plausible explanation of the 
arrangements met with in the diarch type, many difficulties arise in 
connexion with the tetrarch type. For instance, M. Chauveaud’s 1 very 
happy suggestion (abundantly supported in his own work) that there is 
a primary phase of the young seedling characterized by alternate or, as he 
regards it, 4 root ’ structure throughout the plant, while doubtless largely true 
of diarch forms, breaks down according to his own showing in connexion 
with tetrarch forms, the intercotyledonary root poles of which are, according 
to M. Chauveaud, continuous with the 4 elements superposes ’ of the lateral 
strands of the cotyledon. M. Chauveaud does not discuss this type in 
relation to his interesting hypothesis, but it presents the stumbling-block 
here, as also in connexion with the views of Lee, Hill and de Fraine, &c. 
By implication Chauveaud would seem to agree with these latter authors in 
regarding the diarch condition as the more primitive. 
Sargant and Compton, on the other hand, as the result of their investi- 
gations of monocotyledonous and dicotyledonous forms respectively, sum 
up in favour of the tetrarch condition as being the more primitive, at any 
rate for the forms examined. As Compton associates tetrarchy with the 
arboreal and diarchy with the herbaceous habit, and holds that the arboreal 
1 Loc. cit., 1 9 1 1 . 
