Impregnation of Plants. 141 



of different varieties of plants, accompanied with a retrospective 

 view of the progress of the practice, especially in this country. 

 We shall have occasion again to call the attention of our readers 

 to the suhject; and in the meantime, the following extracts will 

 tend to render our remarks more intelligible and plainly under- 

 stood by those who aie not informed upon the subject. The 

 practice of raising new flowers by cross impregnation has just 

 began; and there are probably no limits to the production of va- 

 rieties. 



" Impregnation, in flowering plants, essentially consists in the production 

 of an embryo or rudinientary plant within the ovule,* or l)ofly destined 

 to become the >eex\. Since the ol^ce of the stamens in vegetable repro- 

 duction was indicated by Grew and Riiy, and atterwards clearly estaii- 

 lished by Linnteus, it has been well known that unless some grains of 

 pollen come in contact with the stigma, impregnation does not take 

 place. The seed-vessel may, indeed, continue to grow and ri))en in ihe 

 absence of pollen, and the contained ovules attain the size, texture, and 

 (the embryo excepted) the structure of well-formed seeds; but in such 

 cases a rudimentary plant, which is the essential pan of the seed, is 

 n ver [)roduced. Respecting the immediate origin of the embryo in the 

 animal kingdom, it is well known that three different hypotheses, being 

 all that the nature of the case admits of, were advjinced at an early pe- 

 riod. These several hypotheses have been extended by analogy to the 

 vegetable kingdom. According to one view a germ furnished by the 

 pollen is suj)posed to bo deposited in, and nourished by the ovule: ac- 

 cording to another, the germ is thought either to pre-exist in, or to be 

 originally formed by the ovule itself, and that it is merely excited into 

 action by an influence derived from the pollen: and according to a third, 

 the embryo is conceived to result from the union of a germ furnished 

 by the pollen with another produced by the ovule. f It is hardly 

 probable that we shall ever possess the means of absolutely proving 

 the correctness or demonstrating the fallacy of either of these hy- 

 potheses; but it may be remarked that the first mentioned view, which 

 was advanced at an early period, is the most ditficult to be reconciled 

 either with the phenomena of hybridiry or with the manifest analoiry 

 that exists between seeds and buds; and yet recent discoveries have 

 again rendered it the more probable hypothesis. 



" Soon after the discovery of the oflice of the pollen, several at- 

 tempts were made to explain the manner in which this substance 

 acts upon the stigma. ' Some of the earlier writers, such as Geof- 

 froi and Malpighi, seem to take it for granted that the entire 

 grains of pollen which fall upon the stigma pass down the style quite 



* " The leader is supposed to l)e acquainted generally witli the stnictiiie of the oviilo, a 

 subject upon which tlie limits of the present remarks will not allow me to enter, exrepi to 

 indicate the sources from which the requisite knowledge may be obtained, viz: R. 

 Brown's |)aper on the genus Kingia, with remarks on the stiuciuro of liic unimpregnated 

 ovule; Mtm. snr la geni-ration ft le 'Kvihippcmmt de t'iniht 7j'.n,^c.\i\ Ad. Hiongniart in 

 the 12th vol. of the Annates des Sciences Natureiles ; and, particulai ly, Ni.uffllrs rrchrrhrs 

 sur la slTuctuTP rt le dfvelopprmint de rcvnlc rifif'tal, bv jMiilxl, in the 17lli vol. of the 

 same w^ork. The substance of these memoirs will be fomid in the more recent elementary 

 botanical works." 



t " The latter hypothesis is adopted by Ad. Brongniart with much confidence in his me- 

 moir above cited — ' Dans cet espace . . . . un ou qMel(|ues-uns dcs granules sperma- 

 tiques s' unissent probablement k d 'autres granules fournis par I' ovule pour donner nais- 

 sance au petit globule, premier rudiment inlbrmc de 1' embryo,' &c. Ad. Brcnsniart in 

 Ann, Sci. Nat. 12, p. 254." 



