200 RELATIONS OF OVA AND GEMM.E. 



an abnormality of not unfrequent occurrence. The most con- 

 clusr;e observations are those made by Smith and Braun, 

 on Gcelehogyne ilicifolia, a dioecious Euphorbiaceous plant 

 from Australia, of which the male has never been intro- 

 duced into this country, and in which there is no tendency 

 to the occasional development of stamens. In this plant 

 the maturation of seeds without pollen has now been a 

 subject of notice for upwards of twenty-seven years, and it 

 appears, from the observations of Deecke and Radlkofer, 

 that the structure, both of the ovule and of the mature 

 seed, are perfectly normal, and that the embryo follows the 

 usual course of development, with the exception of the 

 absence of the pollen tube. Radlkofer thus sums up the 

 arguments in proof of a " true parthenogenesis" in this 

 plant : — 



1. The ascertained absence of all male flowers of the 

 same species. 



2. The absence of all indications of hybridization by 

 males of allied species. 



3. The development of the embryo, without any trace of 

 a pollen tube in the ovule. 



4. The stigma not withering, as it always does after 

 impregnation. This mark indicates parthenogenesis in 

 some of the other plants experimented on, especially 

 Cannabis and Mercurialis. The seeds thus raised have 

 never yet given origin to any but female plants. Braun 

 thinks that similar phenomena can be shown to occur in 

 some dioecious species of Chara* 



§ 6. Intermediate between cases such as these, of the 



* Radlkofer, in Annals of Natural History, 2d Ser,, XX., 216. 

 Balfour, in Edinburgh Philosoph. Journal for June, 1858, vol. VIII., 159. 

 Lubbock, in PhUos. Transact, for 1857, page 97. 

 Owen's Address to British Association at Leeds, 1858, p. 26. 

 For Regel's arguments against such Parthenogenesis, see Annals Nat. 

 Hist., 3d Ser., III., 104. 



