RELATIONS OF OVA AND GEMMAE. 199 



certainly compel us to qualify the commonly received state- 

 ments as to the universal dependence of ova, (or bodies 

 having the structure and relations of ova), on impregnation 

 for their farther development. For, though we may con- 

 tinue to hold such to be the only bodies capable of impreg- 

 nation, yet we cannot maintain, with absolute universality, 

 the converse proposition, that every body, having the struc- 

 ture and relations of an ovum, requires impregnation as 

 the starting point of its development ; although we know 

 that, in general, this is so essential, that a mature ovum, 

 if not fertilized, very speedily degenerates, and entirely 

 loses its vitality. In fact, the cases now referred tu 

 — confined, as \nll be observed, to two classes of the 

 Articulata — are the only known exceptions to the non- 

 development of unimpregnated ova in the Animal King- 

 dom. 



§ 5. Similar facts, however, to these have been alleged 

 by botanists from the time of Camerarius (1694). Spallan- 

 zani, Henschel, Bernhardi, Thuret, and many others, have 

 adduced evidence in this direction, and more lately the 

 question has been made the subject of special attention by 

 Mr. John Smith of Kew, and Professor Braun of Berlin. 

 As instances of Plants which occasionally form perfect 

 seeds without access of pollen, Gaertner, Lehocq, and Braun 

 cite certain dioecious species of Zea, Mercurlalis, Cannabis, 

 Spinacia, Bryonia^ Trinia, Datlsca, and Fistacia ; and 

 among monoecious species, the common fig, the Roman 

 nettle, and certain varieties of melon. It appears to have 

 been ascertained that some of these unfecundatcd seeds 

 produce both male and female plants, up to the fourth and 

 fifth generations. At the same time, it is admitted that 

 these observations are not all rigorously demonstrative, for 

 want of due precautions in some of them to prevent the 

 access of pollen from extraneous sources, and to ascertain 

 that no male flowers had appeared among the female ones — 



