452 ORIGINAL ARTICLES. 



was published in the Memoirs of the Academy of St. Petersburg, 

 (VII. Ser. Tome I. No. 2.) He considers that Spallanzani's experi- 

 ments are the only ones which have been well conducted, and admits 

 that if he (Eegel) could have procured perfect seeds by operating as 

 Spallanzani did with the Hemp and the Water-melon, the doctrine of 

 parthenogenesis might be considered established. Eegel attempts 

 to get rid of Spallanzani's authority, by suggesting either that his 

 observations were not carefully conducted, or that Spallanzani did 

 not speak the truth. The latter accusation appears to have no sort 

 of foundation ; at least the grounds for it given by Eegel are of the 

 weakest description. 



In the course of a series of experiments on hybridization, Eegel 

 observed that the anthers of many plants are fully formed and con- 

 tain perfect pollen some time before the opening of the flowers ; 

 from which he concludes that it is necessary, in all experiments on 

 parthenogenesis, to cut off the anthers at a very early period, or 

 otherwise impregnation may have taken place without the observer 

 having any suspicion of it. He considers monaecious and disecious 

 plants to be especially likely to have led to deceptions, because 

 sufficient care was not taken to examine each individual flower — 

 a precaution which is necessary on account of the frequent occurrence 

 of accidental anthers in the female flowers, and because monsecious 

 and dioecious plants produce a greater quantity of pollen than her- 

 maphrodites, and consequently accidental impregnation by wind or 

 insects is highly probable. He considers the Hemp-plant, which has 

 been so much employed for these experiments, to be especially ill- 

 suited for them, on account of the abundance of its easily dispersible 

 pollen, and of its universal cultivation. As therefore (he says) these 

 precautions have not been taken by any trustworthy observer, and 

 as his own observations have afforded only negative results, he con- 

 siders it certain that the formation of a true embryo can only take 

 place under the influence of impregnation. 



Eegel then proceeds to give an account of his observations upon 

 the Cycadese, and especially upon Ceratozamia, and the result that 

 he arrived at was, that no embryo can be formed without the influence 

 of a pollen-tube, but that the growth of the embryo-sac and the pro- 

 duction of endosperm, as also the formation of corpuscula in G-ymno- 

 sperms, may take place independently of impregnation. The case 

 of the CycadcaB he considers very conclusive, as showing that the 

 development in the embryo-sac can only proceed up to the point at 

 which the stimulus to the commencement of the formation of an 

 embryo must be given, and that where this stimulus is wanting, 

 the germinal vesicle, even in vigorous seeds, exhibits no further 

 development. 



Eegel subsequently proceeds to detail his experiments on Mer- 

 curialis annua, from which he concludes that the previous observers 

 who have imagined that they have procured perfect seeds without 

 impregnation, have overlooked the very frequent occurrence of anthers 

 in the so-called female flowers ; and with regard to the persistence 



