ioo Sturch . — Harvey ella mirabilis [Schmitz & Reinke). 
either rests until the end of September, and then commences 
to develop, or the filaments are developed very slowly during 
the summer months. In either case the Harvey ella reaches 
the earliest stage I have yet seen (Fig. i) at the beginning of 
October. Thus it may be said that, as regards its temperature- 
conditions, H. mirabilis commences to develop as the 
temperature falls in the early autumn (average temperature 
at the end of September and the beginning of October was 
1 5*5°), reaches its maximum during the winter months (6°-is&°), 
and gradually dies away as the temperature rises in the 
spring. Specimens found in May are usually partially 
decomposed. Kuckuck’s Choreocolax albus , as previously 
mentioned, bore tetraspores in Heligoland in May. The 
average monthly temperature for May in Heligoland is 8-5° 
(Church’s table), corresponding to the temperature on the 
English south coast for February and March, during which 
months the tetraspores of H. mirabilis are developed. 
During the time when fertilization and copulation of the car- 
pogonium with the auxiliary cell appeared to be most frequent 
— at the end of November — the average temperature was 9-5°, 
Finally, I have to thank Mr. E. M. Holmes for his kind 
help in the identification of the two parasites, and Mr. A. H. 
Church for his valuable advice and assistance. My thanks 
are also due to Professor Vines for his invitation, of which 
I gladly availed myself, to carry out a portion of the work in 
the Laboratory of the Botanic Garden, Oxford. I hope to 
deal with the structure and development of Harveyella 
pachyderma , parasitic on Gracilaria confervoides (Grev.), in 
a future paper. 
