414 ANN BISHOP 



March. All three cultures were quite normal, no experi- 

 ments having been performed upon them to induce con- 

 jugation. There was no appearance of a true epidemic such as 

 Mulsow (21) found in Stentor coeruleus and Stent or 

 polymorphus in May 1911, when he obtained some 2,000- 

 3,000 pairs of conjugants. A few pairs were observed each 

 morning in each culture for about a fortnight, and after that 

 the cultures again became normal. 



For about a fortnight previous to conjugation being observed, 

 microscopic observation of a few individuals taken at random 

 from these cultures had shown that the protoplasm had 

 become dark in colour and somewhat granular in appearance. 

 But the protoplasm of all conjugants observed was of the normal 

 light colour. Whether the protoplasm darkens in colour 

 previous to conjugation and then grows light again when this 

 takes place, or whether individuals destined to conjugate 

 remain light, in which case we must suppose that all such 

 individuals had escaped my observation, I cannot say with 

 certainty. From the fact that in some leaf cultures (see below) 

 the protoplasm of all individuals observed was dark, and that 

 later almost all individuals in the culture conjugated, the former 

 suggestion seems to be the more probable. 



Since all these cultures had been kept at a constant tempera- 

 ture, it was impossible that the sudden rise in room tempera- 

 tures, which took place about the above dates, could have 

 stimulated the Spirostoma to conjugate. 



On May 24 a number of conjugating individuals were 

 observed in one wheat culture and in two leaf cultures which 

 had been kept always at the ordinary laboratory temperature, 

 then about 22° C. The period of conjugation lasted for about 

 ten days. In two of the cultures only a few pairs were found 

 to be conjugating, but in one leaf culture on an average five 

 or six pairs were removed each morning. This gave a fairly high 

 percentage of conjugating individuals. That the cultures were 

 in a good condition was shown by the fact that division took 

 place frequently in the non-conjugating organisms. 



In his paper upon the conjugation of the Stentors Mulsow (21) 



