410 Farmer. — On the Morphology and 
become visible. A further point worthy of note is the dif- 
ference in the endocarp of the two plants, and while this 
perhaps finds its explanation partly in the fact that the ripe 
seeds of the blackberry require more protection than those of 
the ivy, I think this is by no means the whole explanation. 
If the mode of growth which prevails in the two cases be 
compared, it will be seen that they are fundamentally different. 
In Rubus the peripheral cells do not divide, or only to a slight 
extent, but suffer flattening by the expansion of the cells 
interior to them. The effect of this is of course to produce 
considerable pressure on the interior cells, and it is conceivable 
that this pressure might exert a prejudicial influence upon the 
delicate ovule which, but for the presence of the resistent 
endocarp, would be exposed to the full influence of this force 
of compression. As it is, however, owing to the remarkable 
manner in which growth takes place in the cells of the endo- 
carp, the effect of such a pressure on the ovule is entirely 
obviated, and it is able to develop in a free and unconstrained 
manner. In Hedera , on the other hand, the cells of the rind 
are rapidly dividing, and, as we have seen, the internal tissue 
is unable to keep pace with the extension, and its cells are 
rent apart. Consequently the ovules in this plant are not in 
the least subjected to the action of a force like that obtaining 
in Rttbtcs, and hence the early development of a means of pro- 
tection would be superfluous. That the tensions and pressures 
really exist may be easily shown by cutting the fruit across 
and noticing the way in which curvatures take place. Sam - 
bums nigra affords a particularly good example of a fruit 
whose ovule would require protection, since if a longitudinal 
section of moderate thickness be cut through the fruit when 
about half ripe, and if then the hoop which is formed by the 
endocarp be divided at one end, the free ends thus formed at 
once cross over each other and reduce the size of the fruit 
cavity. 
Rubus Idaeus presents essentially the same structure as 
R. fruticosus , except that in this plant the epidermal cells 
grow out into long hairs. 
