12 COMPARATIVE MORPHOLOGY OF FUNGI 



nourishment and are no longer capable of independent development. 

 They proceed in pairs to autophagy, and the product of their fusion 

 acquires a new specific ability for development. 



Under the influence of tendencies which will be brought out in the 

 course of the discussion, the individualization of the gametes in the 

 gametangia ceases at a low stage and the contents of the gametangia 

 remain polyenergid. Thereby the original copulation of gametes is 

 suppressed and replaced by many secondary processes which compensate 

 for the loss of the original merogamy. All these secondary processes of 

 fertilization are called deuterogamy (secondary pairing). In this cate- 

 gory fall the processes of the higher algae and phanerogams (except the 

 lower gymnosperms) while in the animal kingdom the primitive mero- 

 gamy has persisted up to the highest vertebrates. 



In deuterogamy the gametangia assume the function of their daughter 

 cells, the gametes, and cause their coenocytic content to fuse without 

 further differentiation (Fig. 50). A sexual act occurs between two sexual 

 organs instead of between sexual cells, and sexual attraction passes from 

 the latter to the former. This type is called gametangial copulation. 

 It assumes close contact between two gametangia and has a biologically 

 obvious consequence that one gametangium can fertilize only one other 

 which must be located directly next to it; but it has the obvious advantage 

 that it no longer remains to chance whether the two gametes find each 

 other, for the gametangia provide that their nuclei reach each other and 

 fuse. Viewed caryologically, the effectiveness of gametangial copulation 

 becomes greater since most of the nuclei of both succeed in their activity 

 and consequently the number of zygote nuclei increases; viewed numeri- 

 cally, only a small fraction are effective, for the fate of whole gametangia 

 depend on the occurrence or non-occurrence of a single sexual act and 

 only one very strong coenocytic zygote results instead of many smaller 

 unicellular zygotes. There is a special advantage for the gametangium, 

 since at its maturity it is no longer dependent on a definite medium for 

 the copulation of its gametes and consequently it has made possible an 

 easier transition from water to land habitats, and to parasitism in the 

 interior of other plants. Whether gametangia are formed on special 

 branches or whether these branches as a whole complete the act of fertili- 

 zation, they are called copulation branches. In the case of heterogamy 

 they are distinguished as antheridium (male) and oogonium, archicarp 

 or ascogonium (female). 



In the holocarpic forms, gametangial copulation naturally leads to the 

 fusion of whole individuals (Fig. 26, 4 and 5) and is equivalent in a 

 certain sense to self annihilation. This special case of gametangial 

 copulation, in which two mature individuals copulate, is called hologamy. 

 In the fungi, in contrast to certain flagellates, it has doubtlessly arisen 

 secondarily from merogamy. 



