— 110 — 



VI. — The species of Spirogyra présent in Barton's pond 

 show no autumn-phase, which is regardée! as being due to Lhe 

 usual drying up oi' extrême concentration of the water of the 

 pond in tlie suinrnei'-inonths. The présence of S. varians, in 

 1907 alone, is shown to be related to spécial meteorological 

 conditions. Evidence is brought forward to show that tlie exact 

 time of dominance of Zygnemaceae in the spring dépends on the 

 water attaining to a certain degree of concentration. 



VII. — The Desmids in Barton's pond attain their chief deve- 

 lopment after the Zygnemaceous phase is over. It is shown that 

 tlie abundance of development of the Desmids in a given year 

 probably dépends on the degree of dilution of the water, sunshine 

 apparently being the most important factor determining their 

 time of appearance in the yond. 



VIII. — The time of maximum development of the species of 

 Oedogonium in the pond is determined by the first month wilh 

 plenty of bright sunshine. Dilute water is more favourable tu 

 their development than concentrated water. 



IX. — The time of dominance of Microspora during the 

 winter is determined by the lowest winter-temperatures, 

 although compétition with Oedogonium and Conferva also 

 cornes into play. It lias not been possible altogether to explain 

 the frequency-table of Microspora . 



X. — The development of the Confervales in the pond is adver- 

 sely aliected by much bright sunshine. Conferva is also influen- 

 ced by compétition with Microsjiora and Oedogonium. Ophio- 

 ctjtium attains its maximum at the time when the filamentous 

 algal tiora becomes abundant. 



XL — Chaetophora pisiformis is a spring-form, infiuenced 

 in its abundance by the concentration of the water. 



XII. — The Protococcales favour the warmer months of the 

 year, but really high summer- températures affect them adver- 

 sely. lnefjigiata requires higher températures for the attain- 

 ment of its maximum than do the other gênera of Protococcales 

 occurring in Barton's pond. The Protococcales are also influen- 

 ced by the degree of concentration of the water, some (Pando- 

 rina, Sphaerocystis and possibly Jneffigiata) requiring rela- 

 tively dilute, others {Eudorina, Gloeocystis) relatiweiy concen- 

 trated water. 



