284 Causes and Course of Organic Evolution 



stance, indicates that powerful and rapid currents of energy 

 are set up, and that profound stereochemical changes are 

 established immediately after fusion of the conjugate cells, 

 and which render superfluous the need of more than the two 

 cells. 



Sexuality in the Fungi. Reproduction and sex history in 

 the fungi — diversified in the extreme — can only shortly be 

 considered here and now. iVsexual multiplication by cell 

 division, also the formation — as amongst Algae and Protozoa 

 — of akinetes, aplanospores, and swarmspores, reaches its 

 climax of diversity in tliis group. The mode of formation 

 and the structure of sex-cells closely parallel conditions already 

 described for Algse and the Protozoa. 



Thus in Zygochytrium and Polyphagus of the lowly organ- 

 ized Chytridinese, similar or nearly similar tubes are produced, 

 which accurately grow toward each other, fuse, and then unite 

 their contents as in Mesocarpus amongst Algae. Again con- 

 jugation between like non-motile tubes in such conjugate 

 fungi as Piptocephahis, Mucor, or Sporodinia resemble condi- 

 tions seen amongst Algae and Protozoa. 



But amongst the Chytridineae the genus Reesia shows con- 

 jugation of similar motile gamete cells. In this case also, as 

 amongst Algae, the motile gametes are swarmspores, which 

 in other and related genera give rise directly to asexual growths. 

 But here instead they first undergo fusion, and thereafter 

 become asexual resting spores, from which in time a new crop 

 of swarmspores may arise. 



In Zoj)f's genus Lagenidium studies by that observer indi- 

 cate that conjugation may take place between non-motile 

 cells of a thallus, which are neighbor cells of that thallus, or 

 that opposite cells of two distinct thalli may unite. The 

 sexual process also seems to occur only during June, wliile 

 division and asexual spore formation go on dining the other 

 favora})le months of the year. 



Numerous graded transitions can be traced also from such 

 isocon jugate tube-unions to other groups of tlie fungi, such 

 as the Saprolegnieae, where, in its simplest expression, a smaller 



