422 Hill . — The Morphology and Seedling Structure of the 
support this view, for it seems open to doubt whether such evidence is, 
in this case, of very definite phylogenetic value. 
The Monocotyledons, at least the bulbous forms and their near allies, 
are a very highly specialized group of plants which, during a long period of 
time, have adapted themselves very successfully to xerophytic conditions 
with the consequent production of considerable morphological changes. It 
seems only reasonable to suppose that such external changes would be 
accompanied by corresponding modifications of the internal structure, 
so that possibly some of the more striking peculiarities of their internal 
structure may be the outcome of recent adaptations rather than the ex- 
pression of developmental history. 
The adoption of the bulbous habit will, of course, eventually affect the 
seedling structure, and the amount of modification displayed will no doubt 
largely depend on the length of time which has elapsed since its initiation, 
and the degree of perfection which has been attained. The early formation 
of the underground bulb is apparently essential for the geophilous plant 1 , 
and for this purpose the absorbent organ, to be efficient, must be able to 
exert its influence in all directions within the seed (cf. Text-figs. 3-8, 
p. 430). 
To bring about such a state of affairs it is necessary that at the com- 
mencement of germination all other embryonic structures shall be removed 
from the seed as soon as possible ; hence we find the assimilating cotyle- 
don — in a rudimentary condition — with the plumule and radicle is carried 
down into the ground during the first stages of germination (cf. Text- figs. 
7 and 8, p. 420). 
These correlated needs, acting over a long period of time, have been 
the powerful factor in the modification, first of the seedling structure, and 
finally of the embryo itself. The result of this influence has been to cause 
the extreme development of one cotyledon to form a pseudo-terminal 
absorbent organ (Text-fig. 7, p. 420), whilst the other cotyledon — the 
apparently lateral * first leaf ’ — is left to develop from its rudiment outside 
the seed (cf. Text-figs. 8 and 9, p. 420). 
Other Pseudo-Monocotyledonous Dicotyledons. 
In certain other Dicotyledons the geophilous habit has been assumed 2 , 
and in practically all such cases the seedlings are found to be modified 
in the direction of the monocotyledonous ideal. 
To take the well-known case of Cyclamen , the monocotyledonous 
condition has been attained by the almost complete suppression of one 
1 e. g. seeds of Crinum cannot be kept for any length of time, but will germinate and produce 
bulbs and roots in a box without being planted in soil. 
3 A list of such plants is given by Sargant, Ann. Bot., 1. c., p. 7 6 . 
