762 Pearson.—On the Embryo of Welwitschia. 
in their axils tends to confirm the view advanced by Bower 1 and more 
recently supported by Henriques, that they are axillary buds. 
Meantime the mass of the suspensor has greatly increased. The 
growth of the cells of the ‘ lower ring J (x) is seen in Fig. 1, while in Fig. 2 
they already form part of the suspensor. The peripheral cells immediately 
beneath these (Fig. 2 ,y) in their turn behave in the same way, and, as the 
embryonic mass elongates, acropetally developed additions to the suspensor 
are produced until this structure has attained its final form. These later 
formed suspensor cells frequently show a considerable degree of independ¬ 
ence of growth, as was observed by Hooker. 2 Cases are seen in Fig. 1 and 
more markedly in Fig. 3. In both, suspensor-cells with free ends occur ; in 
the latter some are growing parallel with the main body of the suspensor (a), 
others appear to be spreading laterally (d), while two (b) have turned down¬ 
wards and are advancing into the endosperm in the same direction as the 
embryo. This may perhaps be of the nature of a structural adaptation to 
the growing demands of the embryo for food-supplies. In earlier stages, 
while the suspensor is still slender and compact and the embryonic cell-mass 
small, absorption by the cells of the peripheral layers of both regions 
is sufficient. But as they become more massive and the depletion of the 
endosperm advances, the difficulty of maintaining an increasing rate of 
absorption must become greater. The common behaviour of the younger 
suspensor-cells suggests that they have to some extent taken over the 
functions of root-hairs ; morphologically, of course, they are outgrowths 
from the root-cap. 3 At length the suspensor has assumed its maximum 
thickness, and henceforward the surface of the root-cap remains smooth 
(Fig. 4). An interesting and suggestive relation appears to exist between 
the life-conditions of the embryo in certain parts of its course and the 
structure of its suspensor. In early stages, 4 when the young embryonic 
group is growing towards the endosperm, frequently by a route to some 
extent predetermined by the embryo-sac tube, the suspensor is simply the 
elongated hypobasal cell. As soon as it enters the endosperm where 
it meets competing embryos in a narrow area which quickly becomes 
depleted of food supplies, the suspensor thickens. 5 There is very little 
doubt that the embryo which first reaches the starch-bearing region of the 
endosperm 6 normally becomes the embryo of the seed, and, broadly speak¬ 
ing, the more quickly this occurs the greater is the chance that a fertile 
seed will result. A suspensor which has acquired some degree of rigidity 
by reason of the addition to its bulk of several series of peripheral cells, and 
whose more or less spiral form gives to it a certain elasticity, will play an 
important part in assisting the embryo to penetrate the underlying cell- 
1 Bower, 1 . c.; Henriques, 1910. 
3 Cf. Land, 1907, p. 280. 
5 he. p i} pi. 
2 Hooker, 1863, PI. x, Fig. 25. 
4 Pearson, 1909, Text-figure, 
6 1. c.. st. 
