OF FECUNDATION. 



83 



the tubes of the style, although no central canal 

 Bhould exist in it. 



But another question has also arisen out of 

 the subject with regard to the quantity of poUen 

 necessary to effect impregnation. Adanson was 

 of opinion that the smallest possible particle, if 

 conveyed to the ovary, is sufficient. But this 

 opinion is supported by no proof, and is even con- 

 tradicted by later observation ; the merit of hav- 

 ing ascertained the fact seems due to Koelreuter, 

 whose experiments are decisive of the question. 

 The globules of pollen contained in aE the anthers 

 of an individual flower of hibiscus syriacus, were 

 4863, of which fifty or sixty at least were necessary 

 to eifect a complete impregnation. For when 

 the attempt was made with a smaller number, 

 the seeds were not all ripene'd, though those that 

 were ripened were perfect. Ten globules were 

 the least by which the impregnation even of a 

 single seed could be effected in this plant. But 

 in the mirabilis jalappa and longiflora, the 

 flowers of which contained about 300 globules 

 of poUen, two or three were found sufficient for 

 impregnation, as the seed was not improved by 

 the application of more. It was also found that 

 the impregnation of flowers having two or more 

 styles, was completely effected, even when the 

 pollen was applied but to one of them ; which 

 shows that there is a communication between 

 all the stylos, and consequently between all the 

 germens. 



Admitting that the poUen is conducted to the 

 ovary through the channel of the tubes of the 

 style, how after all is the ovary fecundated ; or 

 the seed rendered fertile ? On this subject na- 

 turalists have been much divided ; and accord- 

 ing to their several opinions they have been classed 

 under the respective appellations of ovarists, 

 animalcuUsts, and epigenisists. 



Tlveory of the ovarist. According to the opi- 

 nion of the first class, the embryo pre-exists in 

 the ovary, and is fecundated by the agency of 

 the poUen as transmitted to it thi-oughthe style. 

 This seems to have been the opinion of Grew, 

 who says expressly in his Anatomy of Plants, 

 that when the summits of the stamens open, and 

 the pollen is discharged upon the pistil, some 

 subtil and vivifying efHuvium escapes ; which, 

 descending through the medium of the style, im- 

 pregnates the embryo. Bonnet and Haller seem 

 to have been of the same opinion also, as well 

 as many other eminent naturalists. But the 

 most convincing evidence in support of the opi- 

 nion of the ovarists is that which has been pro- 

 duced by Spallanzani, as founded on a series of 

 observations on the flowers of the spartium 

 junceum. This plant was chosen on account of 

 its producing at the same time flowers in all the 

 difi'erent stages of progress. His first observa- 

 tions were made upon flower buds not yet ex- 

 panded: they seemed to form a compact and 



solid body ; but upon being dexterously opened, 

 the petals, which were yet green, were with some 

 difficulty discovered, then the stamens, and then 

 the pistil. The powder of the anthers was even 

 perceived imbedded in a glutinous substance ; 

 when the pistil was freed from the surrounding 

 integuments, and attentively viewed with a good 

 glass, the pod was also discovered of about 1 -}g 

 line in length. Several protuberances were seen 

 upon its sides ; which, upon opening it longitud- 

 inally, were found to be occasioned by the seeds, 

 which though but small globules, were already 

 discoverable, arranged in their natural order, and 

 attached by filaments to the interior of the pod. 

 Upon dissection, they did not exhibit any ap- 

 pearance of the several parts and membranes 

 into which the mature seed may be divided; but 

 a spongy, homogeneous mass. Flowers in the 

 same state of forwardness were not fully ex- 

 panded till twenty days after. On dissecting 

 buds of a larger size the petals were found to be 

 somewhat yellowish and less compact ; and the 

 powder of the anthers was thrown out by the 

 slightest agitation ; but the lobes and plantlet 

 were not yet perceptible in the seeds. 



On the eleventh day after the flowers had fal- 

 len, that is, after impregnation had taken place, 

 the seeds, .which were formerly globular, began to 

 assume the figure of an heart, attached to the 

 pod by the basis, and exhibiting the appearance 

 of a white point towards the apex. And when 

 the heart was cut open longitudinally, the white 

 point proved to be a small cavity enclosing a 

 drop of liquid. 



On the twenty-fifth day after the flowers had 

 fallen, the cavity was much enlarged towards the 

 base; but was still full of the liquid, in the 

 midst of which there appeared a small and semi- 

 transparent body, of a yellowish colour and 

 gelatinous consistence, fixed by its two extrem- 

 ities to the opposite sides of the cavity. In a 

 month after the flower had fallen, the heart- 

 shaped seeds became kidney-shaped. In forty 

 days after the flower had fallen, the cavity 

 v/as quite filled up with the body that had 

 been generated within it; and which was now 

 found to consist of a thin and, tender mem- 

 brane enveloping the two seed-lobes, between 

 which the plantlet attached to the lower ex- 

 tremity was also perceptible. And hence the 

 seed was now visibly complete in aU its parts. 



From these and a variety of other observations 

 on a number of other species, all of which ex- 

 hibited similar appearances in the generation of ' 

 the seed, Spallanzani concludes that the seeds 

 pre-exist in the ovary before the access of the 

 pollen, by which they are merely rendered fer- 

 tile ; and contends that the embryo, though not 

 previously perceptible, may yet previously exist. 



The theory of the ovarists is supported also 

 by Giertner, who describes the vegetable egg as 



