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THE AMERICAN XATUEALIST [Vol. LIII 



All the recorded, facts concerning hybrid zygospores are 

 in harmony with this observation. 



The male and female nuclei, however, do not fuse until 

 some time later, perhaps two to four weeks. The charac- 

 ter of the zygospore is therefore entirely dependent upon 

 the female parent. This is well brought out hj all the 

 published tigures of h3^brid zygospores as well as by my 

 own observations. After the formation of the fusion 

 nucleus various observers— Chmielewski (1890), Trondle 

 (1907), Karsten (1909) and Kurssanow (1911) {Zpg- 

 nema) — report the occurrence of a double mitosis of 

 which the second division is heterotypic. This results in 

 the formation of four nuclei, of which three degenerate 

 (Trondle, 1911). The degeneration of three of the nuclei 

 has been observed also by Kurssanov in Zygnema. The 

 remaining nucleus becomes the final nucleus of the zygo- 



In a hybrid zygospore, therefore, the first fusion nu- 

 cleus would contain the hereditary factors for the alter- 

 nate characters of both s})ecies; in the subseciuent reduc- 

 tion division and degeneration of three of the nuclei the 

 final zygospore nucleus would contain one of the several 

 possible combinations of these hereditary qualities. The 

 vegetative filament derived from a hybrid zygospore 

 would present some combination of its vegetative charac- 

 ters, such as cell dimensions, number of chromatophores 

 and character of the end walN. The factors for spore 

 characters would not l)ecome visible until it conjugated, 

 and then only the characters cai-ried by the f(Mnale fila- 

 ments would become visible since the spoi-e chai-acters are 

 entirely matriclinal. In tlio adjoining diagram (Fig. 5) 

 the zygospores nre fiuurcd In typical Tortus. The two 

 characters most im]>ortnnt in scp;! r;U inu- the s])ecies are: 

 (1) The dimension- m|' the filMiMcnt v (/.nnms averages 

 about 3;^, (omwHin. nlu.nt J-_M : ( -J ) tlu- Inlcral inflation of 

 the sporifci'dns cell in ranniis in cdntr.-i-r witli the cylin- 

 drical sporilVrou- rcll of < " m hi nn i ^. If we rcpi'esent the 

 factor for th.' .linicn.'M!- .,r '.nm,,.. hy A and of com- 



