REPRODUCTION 459 
the nutritive matter is stored outside the embryo. In 
both cases the root makes its way into the soil by virtue 
of its geotropism and apheliotropism, aided by the move- 
ment 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 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. 
A curious phenomenon is occasionally met with which is. 
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 nor- 
mally exhibit the fusion of particular hyphe and the admix- 
ture of their contents, or gametes, a variation of the pro- 
cess is observed which comes under this category. Instead 
of two gametangia meeting, and their contents fusing, 
to form the zygospore, these organs are developed singly and 
do not coalesce. In this case the fertile cell, which should 
be a zygote, is produced parthenogenetically in each, and is 
known as an azygospore. Another variety of partheno- 
genesis, which resembles the apogamy of the Ferns, occurs 
in Celebogyne, where an embryo is produced in the embryo- 
sac, but without pollination or fertilisation. No sexual cell 
is produced, but there occurs a vegetative budding of one or 
