218 PLANT LIFE 
vegetative activity. Loeb and others have 
shown this to be experimentally possible 
with eggs of various animals; and although it 
has not yet been satisfactorily demonstrated 
in plants, this is largely owing to the very 
small size of the egg, and to its ordinary 
inaccessibility for purposes of this kind of 
experiment. There is no doubt that the 
essential processes are identical in animals 
and plants, and, moreover, we are aware of 
instances amongst the latter in which eggs 
can be stimulated, though by indirect means, 
to grow and develop in the absence of 
fertilisation. 
We do not as yet at all understand—and 
yet this lies very near to the root of the whole 
matter—why the sexual change should pro- 
duce two kinds of states. We speak of these 
states as male and female respectively in the 
higher forms, but there is no detectable 
difference between the gametes of the sim- 
plest organisms. Why there should be this 
difference of state, and why the coalescence 
of two individuals should not only obliterate 
it, but give special vigour to the resulting cell 
we are not as yet in a position to declare. 
As we pass from the lower to the higher 
ranks of the vegetable kingdom, we find 
that the primary physiological differences by 
which sex is first differentiated are betrayed 
by secondary changes which enable the male 
to be distinguished from the female gamete. 
The general trend of the distinction is un- 
