ON THE SEXUALITY OF THE FUNGI. 303 



Enough for our purpose that the knowledge we possess goes 

 to show that sexual reproduction essentially consists in the re- 

 nvigoration of a sluggish mass of protoplasm, by the addition 

 of another and different mass of protoplasm. That an advan- 

 tage is often attained by the latter mass coming from a distant 

 source, is sufficiently evident from what we know of cross- 

 fertilisation generally. 



It now remains to be seen if we can throw any light on the 

 curious disappearance of sexual organs and sexuality in the 

 Fungi — curious, because the sexual process appears to be ail 

 but universal in all organisms excepting the very lowest. 



A hypothesis which suggests itself, and which Eidam favours, 

 and which is certainly supported by some analogies, is to the 

 effect that the apogamous Fungi are not always apogamous. 

 "We know that many forms only produce their sexual organs at 

 comparatively long and rare intervals. The Mucors, for 

 instance, may be propagated through numerous generations by 

 means of the asexual spores ; the sexual organs only arising 

 now and again under favorable conditions. 



Accepting that the sexual process consists essentially in a 

 re-iuvigoration of the protoplasm of the organism, may it not 

 be that one sexual act is effective through long periods and 

 many generations ? Such a view is supported by the known 

 cases of parthenogenesis in other plants, and would explain 

 such cases as the Saprolegnise, if it were placed beyond 

 doubt that protoplasm does occasionally pass through the 

 " fertilising tubes ^^ to the oospheres. 



Moreover, the cases of polyembryony — where several embryos 

 arise in an embyro sac, although only one oosphere is ferti- 

 lised — favour the view that the effect of fertilisation may be 

 extensive ; and we cannot doubt that such is the case wliere 

 adventitious covering branches arise after the conjugation of 

 certain Mucorini (e.g. Mortierella), and in the Orchidese, 

 where fertilisation or even the mere growth of the pollen tube 

 affects the whole flower. 



In other cases, however, great difficulties are experienced. 

 It is not easy to conceive how fertilisation in a distant past has 



