464 



BOTANICAL GAZETTE 



[DECEMBER 



dm 



wide, and 3.5 dm. deep. The boxes were 

 left open on the upper side for a greater part of their length to allow 

 a ballast of rocks to be placed to sink the tanks to the required 

 depth. Any water which might ent< 



removed through the same 



It was found to be an advan- 



tage to have these pontoons extra large in order that the work of 



mi 



from the pontoons rather 

 timbers z cm. bv 10 cm. in 



from 



Cross- 



M iMfl 



■ r 





& ^ 







pHK 

















w^mm 



^raa^p 



Fig. 3 



in place and provided a support for the tanks. It was found neces- 

 sary to place poultry netting of 5 cm. mesh around the finished raft 

 to a height of 3 dm., and in the horizontal spaces between the tanks, 

 to exclude the turtles which infested the water at this place and 

 which proved rather troublesome. These first pontoons proved to 

 be too frail, since they were easily damaged, with consequent 

 submersion of the entire apparatus . They were replaced the fol- 

 lowing year by more substantial pontoons with solid tops. The 

 interior of these was subdivided by four water-tight partitions 

 into five compartments. Through holes in the top provided with 

 corks water could be placed in or taken from the compartments, 

 and it was by this means that the proper level of the tanks was 



