846 FORMATION OF THE FRUIT. 
to the foreign pollen, the seeds thus produced were never 
hybrids. Hybrids appear to be produced more frequently in 
wild plants when the sexes are in separate flowers, and more 
especially when such flowers are on different plants. 
Hybrids are frequently produced artificially by gardeners 
applying the pollen of one species to the stigma of another, and 
in this way important and favourable changes are often etfected 
in the characters of our flowers, fruits, and vegetables. But 
varieties thus produced are not commonly true hybrids, but 
simple cross-breeds. 
The investigations of late years would appear to show that a 
similar law as regards hybridisation occurs in the Cryptogamia 
as in the Phanerogamia. Thus, Thuret has succeeded in 
fertilising the spores of Fucus vesicvlosus with the antherozoids 
of Fucus serratus, an allied species ; but he failed in his attempts 
to fertilise the spores of one genus of the Melanosporeous 
Ale by the antherozoids of another. Other evidence has also 
been adduced as to the hybridisation of the Cryptogamia, and 
there can be little doubt that hybrid Ferns are sometimes pro- 
duced when a number of species are cultivated together, for it 
has been noticed that, under such circumstances, plants make 
their appearance which present characters of an intermediate 
nature between two known species. 
3. Or tHE Frurir.—When fertilisation has been effected 
(see page 295), important changes take place in the pistil and 
other organs of the flower, the result of which is the formation 
of the fruit. The calyx and corolla generally fall off, or if 
persistent, they form no portion of the fruit except when the 
calyx is adherent, asin the Apple (fig. 722), and Quince (fig. 473), 
when it necessarily constitutes a part of the pericarp. The style 
and stigma also become dry, and either fall off, as in the majority 
of cases, or are persistent, as in the Poppy and Anemone ( fig. 700). 
But the principal alterations take place in the wall of the ovary, 
which usually becomes more or less swollen, and soon undergoes 
important chemical changes, and forms the pericarp, either by 
itself (a true fruit), or combined with the adherent calyx or 
other parts of the flower, &c. (a spurious fruit), (see page 296). 
Some pericarps, as already noticed (page 298), are fully developed 
without the fertilisation of the ovules, as those of many culti- 
vated varieties of Oranges, (arapes, Bananas, &c. The fruits 
thus formed, although frequently more valuable than others for 
food, are, of course, useless for reproduction. 
The fruit in its growth attracts the food necessary for that 
purpose from surrounding parts, hence, the fruiting of plants 
requires for its successful accomplishment an accumulation of 
nutrient matter, and is, therefore, necessarily an exhaustive 
process. That the reproductive processes, and especially the 
ripening or maturation of the fruit, tend to exhaust the indi- 
vidual, is proved in various ways. Thus plants which fruit the 
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