400 
POPULAK SCIENCE EEYIEW. 
is no visible penetration of the embryo sac, though it may 
be indented by the pollen-tube. There may be endosmotic 
action in play again here: but speculation is useless; in 
this matter we are for the present foiled, and can no more 
tell why a germinal vesicle, a mere dab of protoplasm, takes on, 
all of a sudden, active growth and evolution, as a consequence 
of the near proximity of the pollen-tube, than we can explain 
the reason for the segmentation of the ovum, which happens as 
a consequence of contact with the spermatozoon. Here we 
must wait patiently for further information. Some observers 
treat these as ultimate facts, and state that we shall get no 
further ; but this is too bold a statement to be received nowa- 
days, as, although there are limits beyond which finite sense of 
reason cannot penetrate, it surely cannot be said that we have 
attained those limits at present. 
The seed, then, it will be seen, is the ovule, with an embryo 
plant developed within it. This is, however, not the whole 
truth, as, during the development and growth of the embryo, 
considerable change takes place in the coats of the ovule. 
Every one must have remarked the astonishing variety in the 
form and appearance of the seed. Hard seeds, soft seeds, 
round seeds, flat seeds, seeds angular, seeds cylindrical, seeds 
as large as an ostrich’s egg (cocoa-nuV), seeds so small that 
they might well be mistaken for grains of dust, seeds as smooth 
as the bore of an Armstrong gun, seeds beset with spines as 
thickly as a hedgehog’s back, seeds pitted like a honeycomb or 
as thickly studded with pimples as Bardolph’s nose, now 
covered with long silky white hair (cotton), in other plants 
invested with thick close felt, or encircled by a membranous 
wing, now nestling in juicy pulp, again wrapped round in a 
fine scarlet mantle or arillus (Nutmeg, Spindle-tree). There is 
really no end to the varied appearances of the seed ; and if, 
to go a step further, the binocular be turned on it, what a 
wealth and variety of form and disposition in the cells of 
its testa or covering, every whit as much diversity in in- 
ternal organisation as in outward conformation I The observer 
who wishes to gain some insight into the variations in the 
structure of the covering of the seed in one natural order 
only, should read Mr. Tuffen West’s paper on the seed of 
Solanacece, and study the author-artist’s illustrative drawings.* 
We must not pursue this part of the subject further, our object 
in alluding to it at all was simply to contrast the uniformity in 
the structure of the ovule with the immense diversity that exists 
in the seed. The range of variation in the one case is enormous, 
* “ Proceedings of Botanical Congress,” London, 1866, p. 182, tables IX., 
