202 RELATIONS OF OVA AND GEMMAE. 



coming an ovule, whose development is dependent on im- 

 pregnation. In such cases it would seem that, though in 

 the normal course of development preference is given to the 

 seed as being the surest means of perpetuating the species 

 in all its integrity, and as possessing a more enduring vi- 

 tality when separated from the parent plant, yet under pe- 

 culiar circumstances, the growing point may be transfonned 

 into a gemma whose early evolution makes less demand on 

 the parental vitality, than the impregnation of the ovule 

 and the formation of the embryo. 



§ 7. Though it is, no doubt, quite exceptional to meet 

 with cases such as have now been cited, in which a body, 

 with the structure and relations of an ovum, either passes 

 into a true gemma, or acquires the power of self-develop- 

 ment characteristic of gemmae, traces of an incipient ten- 

 dency in this direction are not wanting in many cases, in 

 which impregnation is absolutely essential to full develop- 

 ment, and may possibly turn out to be a more frequent 

 characteristic of the sexual elements of both kinds than is 

 generally supposed. Thus though in ordinary cases unimpreg- 

 nated ova do certainly soon lose their vitality, yet they have 

 been seen to make in the interval some abortive attempts, 

 as it were, in the way of development. Thus it has been 

 observed, that, though the unimpregnated spores of Fucus 

 never produce fronds, yet they may put forth irregular pro- 

 longations as if about to germinate.* And so in the un- 

 impregnated ova of animals, the preliminary phenomena of 

 segmentation have been observed by Loven and Schultze in 

 Campanularia.'f by Quatrefage in Hermella and Unio,^ 

 and by Vogt in Firola.^ 



* Carpenter's Comparat. Physiol., 4th Ed., p. 493. (Thuret.) 

 f Quar. Jour. Micr. Sc, III., 65 (from Muller's Archives). 

 X Rambles of a NaturaHst, II., 244, and Comptes Rendus, July 23, 

 1849. 



§ Siebold on Parthenogenesis, 106. 



