512 Annals of the South African Museum. 



004 per cent, sodium chloride, i.e. about twice and three times 

 respectively the normal amount in Kimberley tap-water. 



Most of the collecting was done from Pool I when the pool filled 



and the water was comparatively deep it was from the surface layers 



only; for instance, on 31st January : " The water was about 6 inches 



to 1 foot deep where the collecting was done, and the net was never 



immersed more than 3 inches. The Volvox [i.e. V . Rousseletii] was 



very plentiful, one sweep of the net being sufficient to collect quite a 



quantity." It is possible that the non-motile algae are as a rule not 



actually at the surface but floating in a somewhat lower stratum, and 



that therefore the collecting at the beginning of each phase does not 



present the phytoplankton in its entirety ; at the same time it seems 



improbable that this is the whole explanation of the increasing 



proportion of these algae as the water grows lower. There is certainly 



a continual increase in their number and bulk as the pool ages ; but 



possibly, if deeper collectings were made in the early stages of the 



pool's existence, the number of individuals of these species would be 



found to be more numerous, and a more complete picture of their 



development could be given. As it is they are a sufficiently striking 



constituent of the vegetation of the pool. On the last occasion that 



a collection was made from this pool (2nd April) the gelatinous algae 



are described as forming " a solid mass at the N.W. side of the pool, 



making the water there a vivid green. Eventually, when the pool 



dried up, they formed a thick green layer in several small depressions 



in the mud. The temperature of the water varied from 25 to 30 C. 



during the whole period of collecting. The collecting was usually 



done between the hours of 9.30 a.m. and 12 noon." 



The amount of Volvox often varied in different parts of the pool 

 according to the prevailing wind ; when a strong wind was blowing 

 the Volvox tended to collect at the leeward end of the pool. 



The table on pp. 510, 511 shows the succeeding changes in the pool 

 and its vegetation during the time it was under observation, the 

 latter as shown by the material collected and preserved at each visit 

 to the pool. It must be emphasised that this does not pretend to 

 be the full history of the phytoplankton, since, as the collecting was 

 done entirely with a view to the study of Volvox, no attempt was 

 made to obtain its finer constituents apart from those incidentally 

 collected with Volvox. 



