86 



HISTORY OF THE VEGETABLE KINGDOM. 



reenter, amongst which some will no doubt be 

 suited to all soils and situations. Mr Koiight's 

 experiments of this kind were extended also to 

 wheat ; but not with equal success. For thoug;h 

 some very good varieties were obtained, yet they 

 were found not to be permanent. 



But the success of his experiments on the 

 apple-tree were equal to his hopes. This was 

 indeed his principal object, and no means of ob- 

 taining a successful issue were left untried. The 

 plants which were obtained in this case were 

 found to possess the good qualities of both of the 

 varieties employed, uniting the greatest health 

 and luxuriance, with the finest and best flav- 

 oured fruit. 



Many experiments of a similar nature were 

 tried on other plants also ; from which it ap- 

 peared that improved varieties of every fruit and 

 esculent plant may be obtained by means of ar- 

 tificial impregnation, as they were obtained in 

 the cases already stated. Whence Mr Knight 

 thinks that this promiscuovis impregnation of 

 species has been intended by nature to take place, 

 and that it does m fact often take place, for the 

 purpose of correcting such accidental varieties as 

 arise from seed, and of confining them within 

 narrower limits. All which is thought to be coun- 

 tenanced from the consideration of the variety 

 of methods which nature employs to disperse 

 the pollen, whether by the elastic spring of the 

 anthers, the aid of the winds, or the instrumen- 

 tality of insects. 



But although he admits the existence of vege- 

 table hybrids, that is, of varieties obtained from 

 the intermixture of different species of the same 

 genus, yet he does not admit the existence of 

 vegetable mules, that is, of varieties obtained from 

 the intermixture of the species of different 

 genera ; in attempting to obtain which he could 

 never succeed, in spite of all his efforts. Hence 

 he suspects that where such varieties have been 

 supposed to take place, the fonner must have 

 been mistaken for the latter. It may be said, 

 indeed, that if the case exists in the animal 

 kingdom, why not in the vegetable kingdom ? 

 to which it is perhaps difficult to give a satis- 

 factory reply. But from the narrow limits with- 

 in which this intercourse is in all cases circum- 

 scribed, it scarcely seems to have been the inten- 

 tion of nature that it should succeed even among 

 animals. 



More recent theories. The curious observations 

 of Brongniart respecting the generation of plants, 

 have thrown quite a new light upon this subject. 

 When the grains of pollen arc placed in contact 

 with the surface of the stigma, they project their 

 tubular appendage. The Latter, when the surface 

 of the stigma is naked, insinuates itself more or 

 less deeply within the utricles of the stigma. The 

 granules of the pollen quickly collect near the 

 free extremity of the appendage, which swells 



and assumes a slight degree of opacity. Tlio 

 grain of pollen then shrivels and withers. Soon 

 after, the extremity of the appendage opens, and 

 the granules of pollen are laid bare, and come 

 into contact with the mucilaginous substance of 

 which we have already spoken, and which con- 

 nects the utricles of the stigma. They are there 

 seen in the form of little masses, which succes- 

 sively penetrate to a greater depth in the direc- 

 tion of the style. When the utricles of the 

 stigma are covered by an epidermis, the tubular 

 appendage is applied to the surface of this epi- 

 dermis, and sticks to it by its extremity. Both 

 then open, and the granules of pollen come into 

 contact with the intercellular matter of the 

 stigma. 



The spermatic granules, adds Brongniart, there- 

 fore penetrate into the intercellular intervals of 

 the stigma ; but there they meet with no vessel 

 for their conveyance, as some authors have al- 

 leged. Link thought they were transmitted 

 through the walls of the cellules. Brongniart. 

 on the contrary, says they pass through the in- 

 tercellular spaces. In pcpo macrocarpus, he says, 

 the utricular tissue which connects the stigma 

 and the ovules does not show globules in its 

 intervals previous to fecundation ; but, when the 

 latter has taken place, the brownish streak pro- 

 duced by the spermatic granules may be verj' 

 clearly traced in the yellow utricular tissue, and 

 the granules are seen to reach the ovules. The 

 spermatic granules are never contained in the 

 cellules, but always appear in their intervals. 

 This transmission appears to be effected in con- 

 sequence of the hygroscopic qualities of the 

 granules. When they have thus arrived at the 

 ovule, the granules of pollen penetrate, by the 

 opening which exists in its two membranes, as 

 far as the kernel, passing either directly through 

 the aperture, or, as Brongniart thinks, through 

 a delicate membranous tube, which, issuing from 

 the kernel, applies itself upon the placenta, and 

 there takes up the fecundating granules, to con- 

 vey them into the interior of the ovule. This 

 tube tenninates interiorly at the point where 

 the embryo is to be formed, that is to say, at the 

 vesicle which Malpighi named the sac of the 

 amnios. This vesicle is, as it were, the mould 

 in which the embryo obtains its form. After im- 

 pregnation, there are seen to form in it opaque 

 granules, often of a green colour, which at last 

 form the embryo. The neck by which the vesicle 

 was attached to the sac of the kernel contracts, 

 breaks, and forms the radicle of the embryo. 



Such is the theory of the generation of vege- 

 tables, as resulting from the observations of 

 Needham, Smith, Amici, Robert Brown, and 

 Brongniart. It will be seen to have a great 

 analogy to the same phenomenon as observed in 

 animals. 



This explanation appears to be in accordance 



