208 RELATIONS OF OVA AND GEMMAE. 



In regard to the leiigtli of time for which agamic 2)ropa- 

 gation may run on, our observations are as yet very imper- 

 fect. Lacordaire has followed the parthenogenesis for three 

 generations in Liparis dispar,^ and Davis to the same ex- 

 tent in the Egger Moth ; all the progeny in both cases 

 appear to have been female."|* 



Many plants, it is known, may be propagated by buds or 

 cuttings for a long series of years, without ever flowering or 

 seeding ; in some species of shrubs and trees, which have 

 long been cultivated in our gardens, only one of the sexes 

 is kno^Aai to exist in this country — the Aucuha Japonica 

 and the Weeping Willow are instances in point.j 



§ 1 0. In conclusion, a few remarks may be made on the 

 bearing of these phenomena of " true parthenogenesis" on 

 the theory of alternation of generations. Startling as are 

 many of the facts recorded by Siebold and others, and much 

 as they have tended to modify the opinions formerly held 

 on the relationship of ova and gemmae, they do not seem 

 to be at all opposed to the parallel which has been traced 

 in the different forms of alternation, and the pheno- 

 mena of embryogeny and sexual maturation in the higher 

 species. On the contraiy, they appear to supply the very 

 links wanting to the completeness of the aro-ument. 



Ox O 



caterpillars developed both male and female moths. The inferiority, 

 however, of the organizing force in the unimpregnated eggs was clearly 

 shown by the small proportion in which an embryo was formed, and by 

 its often aborting even when formed ; this, of course, must militate 

 against the perpetuation of the species independently of the sexual act. 

 " True Parthenogenesis," p. 100, &c. 



* Lubbock, in Philosoph. Transact. (1857), p. 96. 



t Siebold on Parthenogenesis, p. 99. 



X Among the lower plants instances of this kind are even more striking. 

 The Gulfweed, which accumulates in such quantities as to acquire for its 

 oceanic habitats the name of " floating meadows," multiplies solely by the 

 detachment of offshoots, and has never been found in fructification (R. 

 Brown, in Annals of Nat. Hist., 2d Ser., VII., 327). So it is also with 

 many mosses, as noticed in Chap. II. 



