iqi;] CUNNINGHAM— SEXUALITY OF SPIROGYRA • 489 



and scalariform conjugation resembles true cross-conjugation in 

 appearance, (3) he has figured cross-conjugation in 3 species in 

 which this appearance would naturally occur, due to this combi- 

 nation, (4) no other observer has reported any of these species in 

 cross-conjugation, the writer feels that there is good ground to 

 doubt the observation of true cross-conjugation by Vaucher. 



Hassall (17) also has figured cross-conjugation, but does not 

 describe it for any of the species thus figured, although he does 

 mention it in the general description of the Zygnemaceae. Figs. 6 

 and 8 of pi. XXIII are reproductions from his plates showing this 

 phenomenon. While Hassall figures and describes cross-conjuga- 

 tion, he nowhere claims to have observed its occurrence. One 

 of the contemporaries of Hassall, in reviewing his book (Hassall 

 18), says "it is unfortunate that the author has not pointed out 

 the cases in which the figures are not the result of his own observa- 

 tions but copied from published plates/' Certain cases are cited 

 in which Hassall's plates were taken from published plates, and 

 these tend to cast some doubt on the source of his plates on cross- 

 conjugation, although they are not among those cited. The 

 writer has been seeking the originals of these borrowed plates, but 

 as yet has not been able to locate them, and is therefore uncertain 

 as to whether or not they exist. Bennett (2, p. 432), in reviewing 

 the general field, says in regard to Hassall "it is quite possible 

 that the statement may be the result of an error of observation; 

 I have often been deceived in this way." Further, Hassall claims 

 to have discovered lateral conjugation, and with this as his basis 

 he lays great stress upon the act of conjugation as being without 

 sex, explaining the movement of the gamete by the "law of 

 universal gravitation" (Hassall 17, p. 132). He gives the 

 following reasons for his belief: (1) both cells are alike; (2) repro- 

 ductive bodies are surrounded by the heavy wall solely for pro- 

 tection; (3) spores arise in the same species, both with and without 

 conjugation; and (4) there is conjugation but "no mixing of the 

 endochrome." As a conclusion he says "thus, so far as can be 

 presumed, the information already acquired would be opposed to 

 the belief in the existence of sex as applied to the cells of Conferoa"* 



3 This genus as used by Hassall included Spirogyra. 



