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Ethel N. Thomas. 
elaborate structure in the successively formed early members. 
This has its advantages and its disadvantages to the student 
of Plant Embryology, for while the early structure remains 
in its appropriate position, even in the mature plant—although, it 
may be, obscured by secondary changes—the stages of development 
are so spread out that the boundaries of embryology are ill-defined. 
In Cryptogams these stages succeed each other in continuous 
development, but in Seed Plants there is a break in development 
due to the arrest of growth following upon the ripening of the seed, 
and corresponding to the interval between this process and that of 
germination. 
The exact stage reached by the embryo in the ripe seed, before 
the arrest of growth takes place, varies considerably, but although 
a rudimentary plumular bud may be differentiated at the apex, the 
members of the embryo are characteristically the cotyledons, hypocotyl 
and radicle. Upon germination these members expand, and their 
tissues become further differentiated. There is theoretically, if not 
in all cases absolutely in fact, a line of demarcation to be drawn 
between this expansion and differentiation of members present in 
the ripe seed, and the production of new members from the 
plumular bud. 
It is to the phase of development concerned with the estab¬ 
lishment of the primary members and their maturation and internal 
differentiation, that the new Embryology is, so far, chiefly directed 
in Phanerogams. The features which appear to be of main impor¬ 
tance for comparative purposes are the characters of the vascular 
system of cotyledons, hypocotyl and primary root, and the mode 
by which the positions of the vascular strands characteristic of the 
one, pass into those characteristic of the other. 
Whether this phase corresponds to the first part of the 
continuously developing embryo of Cryptogams, and therefore, the 
cotyledons to the first leaves, and the hypocotyl to the basal 
portion, of the Cryptogamic stem, can only be decided on compara¬ 
tive internal evidence, although the importance of the results as 
bearing upon the wider phylogenetic issues, is to a great extent 
dependent upon this question. However this may be, Miss 
Sargant’s work on Monocotyledons has shown that the study of 
this phase of development is of phylogenetic value, at any rate 
within the Phanerogams, and the increase of workers on the subject 
proves that it is felt to be a profitable field of research. 
Mr. Tansley and I have been engaged in similar work on the 
