PLANT FOOD a1 
of the effective growth-promoting substances present 
is evident from the following comparison— 
Series I. | Series II. | Series III. | Series IV. | Series V. 
Organic matter added | — 368 97 32 13 
Ratio of total number T 20°6 9°6 34 I'y 
Ratio of total weight I 62°6 29°3 73 26 
The effect of the reduction in amount of organic 
matter with successive fractionation of the bacterised 
peat was also manifest from the general appearance of 
the plants. Those in mineral nutrients only decreased 
in size week by week and became very unhealthy look- 
ing, whilst there was a progressive improvement in 
the appearance of the plants supplied with increasing 
amounts of organic matter. 
In view of these striking differences in general appear- 
ance an examination was made of the internal structure 
of representative plants from each set at the conclusion 
of the experiment. It was found that in all the plants 
receiving organic matter the tissues were more dense 
and the proportion of air spaces to cellular tissue was 
much less than in the control plants. The difference 
was also very marked in the individual cells of the 
respective plants. Those supplied with organic nutri- 
ents were larger and more densely filled with proto- 
plasm, and also contained larger nuclei and more 
numerous chloroplastids. This difference was especially 
noticeable in young newly-formed plants. 
As it is well known that the ordinary distilled water 
used in the laboratory often contains traces of toxic 
