CONSIDERED WITH REFERENCE TO HORTICULTURE. 



7 



live more than two seasons. Hence, the importance of light to plants can 

 scarcely be overrated ; for, while it has been proved that plants, even of the 

 most perfect kind, will live for many months, or even years, in glass cases 

 in which very little change of air has taken place, there is no instance of 

 plants, even of the lowest kind, such as ferns and mosses, living for any 

 length of time without light. Without light there can be no green in leaves, 

 no colour in flowers, and neither colour nor flavour in fruits. 



14. Plants agree with animals in having a sexual system ; but they differ 

 from animals in having for the most part both sexes in the same individual. 

 In the improvement of plants, as in the improvement of animals, the sexual 

 system is a powerful agent ; and what is called cross-breeding is employed 

 with as great advantage in the vegetable as in the animal kingdom. It is 

 remarkable, that the general laws and results by which the process of cross- 

 breeding in both kingdoms is regulated, are the same ; the two parents must 

 be two varieties of the same or nearly allied species, and their qualities may be 

 diff^erent, but must not be opposite ; the preponderating influence, in point of 

 character, is also with the male, and in point of bulk and hardiness with the 

 female, as it is in animals. Many of the finest varieties of fruits, culinary 

 vegetables, cereal grains, and grasses, have been produced by cross-breeding. 

 When cross-breeding is effected between what are considered diff^erent 

 species, the oflBpring is a mule, or hybrid, which, in most cases, is incapable 

 of maturing seeds, and generall}^, in the course of a few yeai-s, degenerates, 

 or reverts to its original parentage. The purple laburnum, which was 

 raised from a seed of the common laburnum, fertilised by Cytisus purpureus, 

 is an example of a true hybrid. The flowers partake of the colours of those 

 of both parents ; and the plant, for two or three years, produced only flowers 

 of this kind, which were never succeeded by seeds ; but in the sixth year, 

 in some plants, and seventh and eighth in others, branches of Cytisus pur- 

 pureus were produced on some parts of the tree, and branches of the com- 

 mon yellow laburnum on others, the latter bearing seed. (See Gard. Mag., 

 vol. xii. p. 225; and Arh. Brit., vol i. p. 590.) There are, however, instances 

 of mules, or true hybrids, producing fertile seeds ; for example, Epiphyllum 

 Mastersiie, raised between Epiphyllum specidsum and Cereus speciosissi- 

 mus, frequently produces perfect seeds, from which plants have been raised 

 partaking of all the characters of the parent hybrid plant. 



15. It would appear, from the case of the purple Laburnum, that a true 

 hybrid or mule cannot always be propagated with certainty, even by por- 

 tions of the plant, or by what is called extension ; since it never can be 

 certain whether the portion taken off^ for propagation will produce the mule 

 or one of the parents. As it is uncertain what are, and what are not, very 

 distinct species, many of the plants originated by cross-breeding, and con- 

 sidered mules, may in reality not be so ; and may, consequently, prove per- 

 manent and improved varieties. Some mules, also, such as that between 

 the sweetwilliam and the common pink, are much less liable to degenerate 

 than others. As some of the most beautiful and useful plants in cultivation 

 are cross-bred varieties or mules, particularly among Geraniums, Heaths, 

 Roses, Gloxinia, &c., the subject well deserves the attention of the amateur, 

 who will find it a source of useful amusement and recreation. 



16. Plants agree with animals in the offspring, when it is raised from seed, 

 bearing a general resemblance to the parent ; but as, in every family, the 

 children of the same parent diff"er individually in features, temper, disposition, 



