CH. Ill] 



LEMNA. 



57 



amount of increase in a given time can be made by 

 counting the fronds ; thus in fig. 10 the culture 8 which 

 has about 21 fronds consisted originally of six separate 

 fronds, as shown in culture W. 



We grow the Lemna in narrow cylinders containing 300 

 c.c. of fluid ; if the cylinders are darkened by black card- 

 board covei-s the cultures keep reasonably free from algse. 



Fig. 10 gives the result of an experiment carried on in 

 a greenhouse in the winter. Three jars 8, K, W, were 

 prepared, in each of which six fronds were placed. S 

 contained 0'25 "/o Sachs' culture fluid: K contained 

 0'257o potassium nitrate, while W contained only distilled 

 water, a drop of dialysed iron being added to each 

 culture. The amount of increase is shown in the figure, 

 the difierence in root production as well as in the amount 

 of frond is noticeable. In this and similar experiments 

 the Lemna died in a short time in distilled water; 

 whether this is due simply to starvation we have not 

 ascertained. 



FiQ. 10^. Exp. 77. 



