110 



THE AMERICAN NATURALIST 



[Vol. LIU 



species: *S'. communis X *S'. rarinns from one locality, 8. 

 variant X aS'. porticdlis from two localities, and S. max- 

 ima X 8. suhmaxim<i from one locality. 



The phenomenon of hyhridization in this o'enus is evi- 

 dently (piite rare, as shown l)oth by the small number of 

 references to it in the literature and l)y the few cases 

 that liave come under niy observation. From the collec- 

 tions ma<le in Illinois, ^ia--achusetts, ^[ichigan, Ohio and 

 New Yoi'k, I have sf)-! i-ccords of conjugating Spirogyras 

 and only five records of conjugation between different 

 species from four localities, all in central Illinois. 



In tliis paper I wish to record, not only the finding of 

 conjugation between species, but what seem to be the 

 progeny of such crosses. It lias been found impossible 

 to cultivate these fonns in the laboratory so that there 

 is no experimental proof of their origin. Nevertheless, 

 they have been found associated w^ith filaments that were 

 crossing and with filaments of the two parent species that 

 were conjugating normally. There were few other spe- 

 cies present in these collections, and there are no species 

 in central Illinois that could ]-)0ssibly ])e confused with 

 them. Tender the circmnslniKM's it seems i iii])ossible to 

 account for th(^ >tr;nmc niixliirc of fortiis in tlicse five col- 

 lections except on the l);i>i> of a hybrid oi'i-in. 



Spirorn/ra rariaus X S. communis 

 In collections taken from Campus Creek, two miles 

 southwest of Charleston, 111., during the latter part of 

 May, 1913, specimens of typical S. varians and S. com- 

 munis occur together with filaments that resembled one 

 or the other of these species l)ut whose dimensions ex- 

 clude them fi'om these species. In going over these col- 

 lectioiis in l*.*!.") lihnneiit s of rtiridiis were found conjuga- 

 tiim- with ( (niniiiiinsrAud hybrid /yuospores were found in 

 both kiii.N ol" filnmcid^. Tlii^ Miu-'cvted that the unnam- 

 ahlc form- were the pi-duciiy of liylirid zygospores. 



■V. >a,nn,. ha- v.-rtiii ix (•cjU .:!(> 40 fi X 30-120 a 

 single chi'omatophore making one to five turns in the cell. 



