446 REPRODUCTION. 



1144. Apogamy. The prothallus which develops from a fern- 

 spore bears upon its under side the sexual organs ; from their 

 interaction a bud is produced which grows into the fern-plant. 

 Farlow 1 has shown that in some cases the prothallus can give rise 

 to a bud without sexual intervention. De Bary 2 has traced out 

 the connection between this mode of budding and that which is 

 found in certain other plants. To the abnormal budding of the 

 prothallus and homologous structures he has given the name 

 apogamy. 



1145. Parthenogenesis 3 is the production of an embiyo with- 

 out the intervention of pollen (or the equivalent of pollen in the 

 lower plants). Coelebogyne ilicifolia, a species belonging to the 

 order Euphorbiaceae, has been known to produce seeds with more 

 than one embryo, and without access of pollen. It has been 

 held by some that the embryos in this case are formed from 

 oospheres which had not been fertilized, but investigations by 

 Strasburger indicate that they are adventitious outgrowths from 

 the cellular tissue of the nucellus, and are outside of, not in, the 

 embryo-sac. 



In some other cases examined, Strasburger regards the forma- 

 tion of embryos outside the embiyo-sac as dependent upon the 

 fertilization of the oosphere, but in only one case of this kind 

 did he observe any embiyo form also from the fertilized oospore. 



1146. Polyembryony, the production of two or more viable 

 embryos in a seed after the manner just described, is of frequent 

 occurrence in oranges, onions, and Funkia (Day Lily). 



1147. Fertilization in different degrees of consanguinity. It has 

 been shown in Volume I. that " no two individuals are exactly 

 alike ; and offspring of the same stock ma}' differ (or in their 

 progeny may come to differ) strikingly in some particulars. 80 

 two or more forms which would have been regarded as wholly 

 distinct are sometimes proved to be of one species by evi- 

 dence of their common origin, or more commonly are inferred 



1 Quart. Journ. Mie. Science, xiv., 1874, p. 266 ; Proceedings Am. Acad., 

 ix. p. 68. 



2 Botanische Zeitung, 1878, p. 449 et seq. 



3 Braim: Ueber Parthenogenesis bei Pflanzen, 1857; Hanstein : Die Parthe- 

 nogenesis der Coelebogyne ilicifolia, 1877 ; Hanstein : Botanische Abhand- 

 lungen, 1877 ; Strasburger : Befruchtung und Zelltheilung, 1878. 



Cases of parthenogenesis occur in the lower plants, where they have been 

 followed out in cultures continued for a considerable time. Their consideration 

 belongs to the next volume of this series. 



For an account of parthenogenesis in animals, see Balfour : Treatise on 

 Comparative Embryology, 1880 ; also Brooks on Heredity, 1883, p. 55. 



