Varietäten, Descendenz, Hybriden. 
295 
the embryology within the embryo sac is less conclusive. Compari- 
son with Gymnosperms establishes a presumption in favour of two 
cotyledons among the primitive Angiosperms. The development of 
the embryo within the embryo sac, however, gives no decided clue 
to the ancestral form. This is not unnatural when we consider the 
conditions which affect the shape of the developing embryo: — 
1. The space at its disposal, depending partly on the shape of 
the embryo-sac, and partly on the development and texture of the 
endosperm. 
2. The method of food supply. 
3. The configuration of the mature embryo, — that is of the 
embryo immediately before its exit from the seed. This again de- 
pends on two sets of conditions: the future form of the seedling which 
is largely determined by its environment after germination, and the 
method by which the embryo will free itself from the tissues of 
the seed. 
But the embryology is not concluded when the seed is left be- 
hind, — the history of the embryo after germination yields us 
a fresh dass of evidence. The embrjm is less cramped when it has 
escaped from the seed, and the development of vascular tissue gives 
rigidity to its form. Ancestral features, if reproduced after this epoch, 
stand a better chance of being preserved. The seedlings of Monoco- 
tyledons and Dicotyledons have been examined of late years with a 
phylogenetic aim. From the comparison of the several types of vas¬ 
cular symmetry, a primitive type has been arrived at in the case 
of each dass, and these two primitive types resemble each other 
very closely. The points which they have in common represent, no 
doubt, the seedling structure of the Primitive Angiosperms. 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 An- 
giosperm was dicotylar. 
Assuming that the seedling of the Primitive Angiosperms was 
dicotylar, we have to account for the origin of Monocotyledons. 
Professor Henslow has proposed the theory that Monocotyledons 
have been derived from Dicotyledons by suppression of one cotyle- 
don and adaptation to an aquatic habitat. After criticising this theory 
the author brings forward the view that the fusion of cotyledons which 
gave rise to the early Monocotyledons was an adaptation to the 
geophilous habit. Geophilous plants are species which have their 
permanent axis Underground. The more specialised geophytes are 
natives to climates in which a short season of growth is followed 
by a long period in which the conditions are unfavourable to Vege¬ 
tation. Such are Alpine and Arctic situations, where the summer 
may not last three months, and the ground is buried in snow for at 
least nine: or dry climates with periodic rains, as in the South 
African Veldt, and in localities of the mediterranean region. Geo¬ 
phytes form a large proportion of the flora in such climates. The 
linear leaves of Monocotyledons are particularly well adapted to sudden 
elongation in order to pierce the soil in the spring, when the 
ground is moist with meltings now, or the first rains. Another feature 
characteristic of the geophyte is the long interval which commonly 
elapses between the sowing of its seeds and their germination, which 
is correlated with the immature condition of the embryo in the ripe 
seed. The plant has a struggle to get the seed ripened at all within 
its short growing season. To place the germ of the future plant in 
