SYNGAMY 



229 



Fungi. — The fusion of the sexual elements described in the preceding 

 chapter (p. 199) proceeds as follows. In Synchytrium the morphologically 

 similar uniciliate gametes unite to form a zygote which penetrates into a 

 host plant. In Monohlepharis the uniciliate male gamete creeps along the 

 surface of the oogonium to its opening, where, after loss of its cilium, 

 it unites with the egg to form a resting oospore ; this matures either inside 

 or outside the oogonium. In Albugo Candida and Pythium Deharyanum 

 the egg is entered by a single male nucleus through a conjugating tube 

 from the antheridium (Fig. 139, B). The nuclear fusion in Pythium 

 and Achlya occurs in association with a cytoplasmic "coenocentrum" 

 (P. Patterson). In Saj)rolegnia, which has several eggs in the oogonium, 



y^ >i 





A B C 



Fig. 139. — A, Syngamy in Polysiphonia; group of paternal chromosomes about to enter 

 female nucleus. {After Yamanouchi, 1906.) B, Syngamy in Albugo Candida; female 

 nucleus in ooplasm near coenocentrum (larger dark body) ; antheridial tube about to dis- 

 charge male nucleus. {After Davis, 1900.) C, Syngamy in Lygodium palmatum. The 

 coiled nucleus of the functional spermatozoid lies against the right end of the egg nucleus, 

 while its cilia lie in the cytoplasm near by. Outside the egg are other spermatozoids. 

 Arrow indicates neck canal. (After Rogers, 1926.) 



the antheridium sends in a branching tube which delivers a male nucleus 

 to each egg. 



In the zygomycetes® the contents of the multinucleate gametangia do 

 not subdivide into small gametes but meet and fuse in their entirety. 

 The product is a heavy-walled zygospore. The extreme minuteness of 

 the nuclei and the abundance of metabolic products in the protoplasm 

 have so far made it impossible to clear up the matter of nuclear behavior 

 in this group. 



In the higher ascomycetes the sex organs are typically antheridia and 

 ascogonia. Some species have both organs, some have one or the other, 

 and some have neither. In some cases the organs are uninucleate and in 

 others multinucleate. After an ascogonium has been entered by the con- 

 tents of an antheridium the nuclei do not fuse (according to one prevalent 

 view) but associate and divide repeatedly in pairs ("conjugate division" 



« P. A. Dangeard (1906), Moreau (1911, 1913, 1915), Keene (1914), Burgeff (1915), 

 Macormick (1912), Baird (1924). 



