REPRODUCTION 449 
stored outside the embryo. In both cases the root makes 
its way into the soil by virtue of its geotropism and aphe- 
liotropism, aided by the movement of circumnutation, and 
by the adhesion of the root-hairs to particles of the soil. 
In some Monocotyledons the upper part of the single 
cotyledon remains in the seed and absorbs the nutriment 
from the endosperm, while its base elongates and thrusts 
the young plant downwards. 
Sometimes the usual alternation of sexual and asexual 
reproduction in the higher plants is interfered with by the 
substitution of the vegetative method for one of them. In 
the phenomenon of apospory, noticeable in some Ferns, we 
have small prothallia developed on the back of the leaves 
in the place of spores. This is a case of the production of 
a bud instead of an asexual cell. Apospory is also known 
to occur among the Mosses. 
In the Ferns, again, the sporophyte sometimes arises 
as a bud or vegetative outgrowth upon the prothallium, a 
phenomenon known as apogamy. 
There is another kind of apogamy known, which is 
generally termed parthenogenesis. It occurs among the 
Fungi, where, as in Saprolegnia, oospheres are formed in 
oogonia, which do not become fertilised, and yet have the 
power of growing out into new plants. In some species of 
Mucor which normally exhibit the fusion of particular hyphe 
and the admixture of their contents, or gametes, a variation 
of the process is observed which comes under this category. 
Instead .of two gametangia meeting, and their contents 
fusing, to form the zygospore, these organs are de- 
veloped singly and do not coalesce. In this case the fer- 
tile cell, which should be a zygote, is produced partheno- 
genetically in each, and is known as an azygospore. 
Another variety of parthenogenesis, which resembles the 
apogamy of the Ferns, occurs in Cwlebogyne, where an 
embryo is produced in the embryo-sac but without pollina- 
tion or fertilisation. No sexual cell is produced, but there 
occurs a vegetative budding of one or more of the cells 
29 
