20 EXPLOITATION OF PLANTS 
the phosphotungstic acid fraction of bacterised peat. 
The proportions of organic matter thus added in Series 
II, III, IV and V were respectively only 368, 97, 32 and 
13 parts per million of culture solution. 
Twenty plants of Lemna minor, as nearly uniform as 
possible in size, general healthiness and root develop- 
ment, were counted out into each of the fifty dishes. 
The solutions were changed twice each week, and 
the plants in each dish were counted once every 
week, 
The plants in all the series multiplied fairly uniformly 
for the first week, then the effect of the added organic 
matter became very marked, until at the end of three 
weeks the plants in Series II and III completely filled 
their dishes. At this stage the plants in all fifty dishes 
were halved, one-half being retained in the dish to con- 
tinue the experiment, and the dry weight of the other 
half estimated. This was repeated each week during 
the continuation of the experiment. 
The average figures obtained for the total number of 
plants derived from the original twenty in each series, 
and their total dry weight at the end of six weeks, are as 
follows— 
Series I. | Series IJ. | Series III. | Series IV. | Series V. 
Number from original 
BO pices ot cin seal teas 
Dry Weight (in mg.) 
‘from original 20 .| 17°6 II03 516 129 46 
326 6723 3124 1100 483 
The fact that successive fractionation of the extracts 
obtained from bacterised peat resulted in a diminution 
