SECT. II 



PHYSIOLOGY 



303 



would be degraded to organs of vegetative multiplication. The adventitious 

 germs in the polyembryonic seed are, however, so far dependent upon sexual 

 reproduction, that for the most part they only attain their development in case 

 pollination has previously taken place ; but in Coelebogyne, one of the Australian 

 Euphorbiaceae, of which usually only female specimens are found in cultivation, 

 and in Bcdanophora elowjata and Elatostema acuminatum according to TREUB, 

 and Bal. ylobosa according to LOTSY, the adventitious germs develop without the 

 stimulus of fertilisation. These plants accordingly afford examples of APOGAMY, 

 or of the substitution of a vegetative for a sexual mode of reproduction, such as 

 /M-i-urs in certain ferns. 



In the apogamous ferns vegetatively produced plants arise on the prothallus 

 in the position of the sexual organs. This is found in different degrees in 

 Athyriurnjilixfcmina, var. cristata, As- 

 pidium falcatum, Todea africana, Pteris 

 cretica, and in Ncphrodiwn pseudo-mas. 

 var. polydactyla. In the latter examples 

 the sexual organs are no longer formed, 

 although the young plants arise, by a 

 vegetative process of budding, from 

 exactly the same part of the prothallium 

 where the archegonia would have been 

 developed. FARMER, MOORE, and DIG BY 

 have shown that in Nephrodiumfae origin 

 of the apogamous bud is preceded by fusion 

 of nuclei of vegetative cells of the pro- 

 thallus. In the case of Aspidium filix 

 mas. var. cristatum, etc., the apogamy 

 seems to have resulted from cultivation. 

 In a broad sense the development of 

 bulbils in the place of flowers, in the 

 species of Allium, might be considered 



Kiu. :i4u. Vegetative formation of embryos in 

 Funkia ovata (Hosta coerulea) by the budding 

 of the nucleus ; n, nucellus with cells in 

 process of forming the rudiments (ae) of the 

 adventitious embryos ; S, synergidae ; E, egg. 

 cell, in the lower figure developing into a sexu- 

 ally-produced embryo ; if, inner integument 



as an example of apogamy ( 106 ). 



The cases of parthenogenesis de- 

 scribed in recent years among the higher 

 plants (Compositae, Alchemilla, Thalic- 

 Irum, firyonia ?) may be regarded as 

 examples of a further peculiar type of 

 apogamy. The ovum develops into an embryo without fertilisation, but since 

 the reduction division has been omitted from the processes leading to its differ- 

 entiation the egg cell has in these cases lost the characteristics of a female 

 sexual cell and corresponds to a purely vegetative cell. The same will probably 

 be found to be the case in Wikstroemia indica, Ficus hirta, and Chara crinita which 

 are also parthenogenetic ( 107 ). 



In some cryptogamic plants (Marsilia, Saprolegnia) as among 

 lower animals, true parthenogenesis occurs. LOEB found that solu- 

 tions which withdrew water (MgCL,, other salts, sugar, urea) could 

 stimulate the ovum to parthenogenetic development. WINKLER used 

 extractives derived from the sperm, while NATHANSOHN showed that 

 sometimes a rise of temperature could interrupt the resting state of 

 an ovum awaiting fertilisation and lead to a parthenogenetic develop- 



