The Life of the Plant. 183 
two belong to nearly related species. The peach can be 
grafted on a plum-stock, but not the rose on an oak. 
Reproduction by means of oospheres or germ-cells 1s es- 
sentially different from the modes already described ; since 
here cells of two different kinds are necessary to produce 
the new plant by their mutual action the one on the other, 
the cells of each kind having no power of propagation in 
themselves alone. This process of mutual action is called 
fertilisation or impregnation, and involves a distinction be- 
tween the fertilising or made, and the fertilised or female 
element. ‘This latter becomes, after fertilisation, the germ 
of the future plant. 
Of the yarious processes of fertilisation we can here only 
describe that which is characteristic of all flowering plants 
= | or Phanerogams. The organs of re- 
production—the male follen, and the 
female ovu/e—are in them collected in 
the flower, and form its essential con- 
stituents, and the process of fertilisation 
consists in the pollen exercising an 
influence on the ovule, by which a 
further development is induced in the 
latter. In those plants in which the 
ovules are enclosed in an ovary it is 
Jura; © Cuphea platy necessary that the pollen should, in the - 
centra; D Diéipsacus j 
Yullonum; © pollen- first place, fall upon the stigma. The 
masses (pollinia) of Cyn- é : 
eee Pg os period of maturity of the pollen and of 
(Asclepiadez : Ae ; 
the capacity of the ovule for fertilisation 
generally coincides with that of the expansion of the flower. 
The anthers then open, and the pollen-grains (Fig. 355) are 
’ 
