OK FECUNDATION. 



8/5 



from the secils now produced was more like a 

 paniculata than formerly ; and when the experi- 

 ment was continued through several successive 

 generations, it was at last converted into a per- 

 fect paniculata* 



This is thought to be an infallible demonstra- 

 tion of the truth of the doctrine of the epigen- 

 isists. But why may not the pollen of one spe- 

 cies of plant be allowed to produce some particu- 

 lar change upon the development of the embryo 

 of another species, although that embryo should 

 be supposed to have pre-existed in the ovary ? 

 The action of the pollen thus introduced must 

 amount to something ; and it is just as difficult 

 to conceive how an individual, whether proper 

 or hybrid, should be generated from the union of 

 the seminal principles of two plants of the same 

 or of a different species, as from the peculiar 

 effect of the pollen of the same, or of a different 

 species, upon an embryo already existing. But 

 the doctrine is yet liable to a much more serious 

 objection ; for if the seed is generated from the 

 union of two fecundating principles which form 

 an intermediate offspring, then female plants of 

 the class diwcia ought occasionally to produce 

 seeds whose offspring shall be hermaphrodite, or 

 ut least monmcious, which was never yet known 

 to happen. 



Although the arguments of the epigenisists are 

 by no means satisfactory, yet it cannot be denied 

 that hybrid productions partake of the proper- 

 ties both of the male and female from which they 

 spring. This was long ago proved to be the fact 

 by Bradley, and more recently confirmed by 

 the experiments of Mr Knight; as well as 

 happily converted to the advantage of the culti- 

 vator. Observing that fanners who rear cattle 

 improve the progeny by means of crossing the 

 breed, he presumed from analogy that the same 

 improvement might be introduced into vege- 

 tables. His principal object was that of procur- 

 ing new and improved varieties of the apple and 

 pear, to supply the place of such as had become 

 diseased and unproductive, by being cultivated 

 beyond the period which natxire seems to have 

 assigned to their perfection. But as the neces- 

 sary slowness of all experiments of the kind, 

 with regard to the fruit in question, did not keep 

 pace with the ardour of his desire to obtain in- 

 formation on the subject, he was induced to in- 

 stitute some tentative experiments upon the com- 

 mon pea, a plant well suited to hispurj)Ose, both 

 from its quickness of growth, and from the 

 many varieties in tbrm, size, and colour, which 

 it afforded. In 1787, a degenerate sort of pea 

 was growing in his garden which had not re- 

 covered its former vigour even when removed to 

 a better soil. Being thus a good subject of ex- 

 periment, the male organs of a dozen of its im- 



Wilitenow, p. 3-28. 



mature blossoms were destroyed, and the female 

 organs left entire. When the blossoms had at- 

 tained their mature state, the pollen of a very 

 large and luxuriant gray pea was introduced into 

 the one half of them, but not into the other. The 

 pods of both grew equally ; but the seeds of the 

 half that were unimpregnated withered away, 

 without having augmented beyond the size to 

 which they had attained before the blossoms ex- 

 panded. The seeds of the other half were aug- 

 mented and matured as in the ordinary process 

 of impregnation ; and exhibited no perceptible 

 difference from those of other plants of the same 

 variety, perhaps, because the external covering 

 of the seed was furnished entirely by the female. 

 But when they were made to vegetate in the 

 succeeding spring, the effect of the experiment 

 was obvious. The plants rose with great lux- 

 uriance, indicating in theirstem,leaves, and fruit, 

 the influence of this artificial impregnation ; the 

 seeds produced were of a dark gray. By im- 

 pregnating the flowers of this variety with the 

 pollen of others, the colour was again changed, 

 and new varieties obtained superior in every res- 

 pect to the original on which the experiment 

 was first made, and attaining, in some cases, to a 

 height of more than twelve feet. In these ex- 

 periments it was observed that the plant had a 

 stronger tendency to produce coloured blossoms 

 and seeds than white ones. For when the pol- 

 len of a coloured blossom was introduced into a 

 white one, the whole of the future seeds were 

 coloured. But when the pollen of a white blos- 

 som was introduced into a coloured one, the 

 whole of the future seeds were not white. 



Mr Knight thinks his experiments on this 

 subject afford examples of superfetation, a jihe- 

 nomenon the existence of which has been ad- 

 mitted amongst animals, but of which the proof 

 amongst vegetables is not yet quite satisfactory. 

 Of one species of superfetation Mr Knight had 

 certainly produced examples ; that is, when, by 

 impregnating a white pea blossom with the pol- 

 len both of a white and gray pea, white and gray 

 seeds were obtained. But of the other species 

 of superfetation in which one seed is supposed to 

 be the joint issue of two males, the example is not 

 quite satisfactory. Such a production is perhaps 

 possible, and further experiments maj^ probably 

 ascertain the fact ; but it seems to he a matter 

 of mere curiosity, and not ajjparently connected 

 with any views of utility. But the utility of 

 the experiments, in as far as they show the 

 practicability of improving the species, is very 

 obvious. And the ameliorating effect is the same 

 whether by the male or female ; as was ascer- 

 tained by impregnating the largest and most 

 luxuriant plants with the pollen of the most 

 diminutive and dwarfish, or the contrary. By 

 which means any number of varieties ma}' be 

 obtained, according to the will of the ex])e!i- 



