XII.] CONJUGATION AND SEXUAL REPRODUCTION. 169 



means ensured, that the number of ids is halved, and that their 

 fresh grouping is thereby provided for, we cannot at any rate 

 predict whether the process is conducted in precisely the same 

 way as in animals. We ought perhaps rather to expect that 

 some deviation from the reducing methods customary among 

 animals would here be met with, a deviation which would render 

 the meaning and significance of the latter even clearer and more 

 definite. 



We are justified, however, in believing that, in the cases of 

 plant parthenogenesis, the amount of variation will diminish, 

 together with the capability of adaptation by the operation of 

 natural selection. Adaptations caused by direct influence on 

 the germ-plasm are naturally conceivable in these as in other 

 cases, but at present we know so little about such changes, 

 whether produced by climatic or nutritive conditions, that it is 

 impossible to determine how much may be implied by them. 



Ten years ago parthenogenesis was doubted by botanists, or 

 at any rate was regarded as very rare, and only to be found in 

 cultivated plants, such as Pferis eretica, in which a certain ten- 

 dency to degenerate was recognizable, or, at any rate, in which 

 the structural and functional arrangements were no longer 

 subject to the operation of natural selection. But we now 

 recognize that a whole group of fungi, the Saprolegniae, ' in- 

 cluding several genera and many species, are parthenogenetic' 

 Among the Ascomycetes ' it is admitted that many genera and 

 species . . . are certainly asexual.' Amphigonic reproduction 

 in the iEcidiomycetes is ' extremely doubtful,' while the Ba- 

 sidiomycetes ' afford an example of a vast family of plants, of 

 the most varied form and habit, including hundreds of genera 

 and species, in which, so far as minute and long-continued 

 investigation has shown, there is not, and probably never has 

 been, any trace of a sexual process ^' 



If the last statement be correct, it is impossible to maintain 

 the existence of parthenogenesis in the Basidiomycetes ; for 

 this method implies the sexual reproduction of ancestors 

 as its origin. Parthenogenesis is virgin reproduction, and 

 signifies a power of development without fertilization pos- 

 sessed by female germ-cells. Parthenogenesis has arisen from 

 bisexual reproduction by the elimination of the male and 

 ^ See Vines in ' Nature,' 1889 (Oct. 24), p. 626. 



