730 
Thomas . — Seedling Anatomy of 
Leguminosae and by Lee in the Compositae. Such forms are to be found 
in the groups described in this paper (e. g. Liriodendron , Decaisnea , &c.), 
even in the Ranunculaceae, and I am in complete agreement with Lee when 
he says, ‘ Although there are two extremes — diarch and tetrarch — all stages 
from the one to the other have been' described in the preceding pages,’ 1 and 
what is true of the Compositae is true, I think, in general. It is interesting, 
however, to note that while Compton and Lee agree as to the close 
connexion between what I have termed the diarch and tetrarch varieties of 
the cruciform type, they differ fundamentally as to the relative primitiveness 
of these conditions. While Compton pronounces in favour of the primitive- 
ness of tetrarchy, Lee regards the seedling anatomy of the Composites as 
founded upon the diarch condition, the tetrarch and the intermediate forms 
being produced in relation to size of seedling and other factors. 
It should be clearly borne in mind that the intermediate cases instanced 
Cruciform Type - Diarch variety 
Text-fig. 42. 
by me in 1907 — of which Mr. Lee says, £ If there are cases, as Miss Thomas 
assumes, where the tetrarch structure is becoming reduced to diarch ’ — fall 
within precisely the same category of phenomena as those of which he 
remarks, ‘ There are as certainly seedlings in which the diarch structure is 
giving place to tetrarch \ 2 It is important that it should be fully realized that 
there is only one set of phenomena in question, but of these there are two 
distinct interpretations. 
Mr. Lee’s conclusion that ‘ tetrarchy and diarchy have probably been 
interchanged several times during the evolution of Angiosperms’ is quite 
unnecessary if, as seems indicated, he suggests it to account for different 
phenomena, but it may well take its place as a useful and suggestive contri- 
bution to the theory of the subject. His view would seem to be that the 
process of evolution of the diarch and tetrarch forms is a ‘reversible one’. 
This is a tenable hypothesis if we can with any measure of plausibility 
deduce a reasonable concept of the components, even though the factors 
directing the action — » or <— await discovery. One thing is certain, that we 
1 Loc. cit., p. 323. 2 Loc. cit., p. 325. 
