232 Journal of Agricultural Research v 0 i. xxvi, no. 5 
weighings and the addition of distilled water during the time the plants 
were making their growth. The plants on the right represent a slightly 
more vigorous growth than those on the left. The plants on the left 
differed most from those on the right by the branches and leaves at the 
top becoming chlorotic a short time before the photograph for C was 
made, whereas those on the right maintained a normal green color. 
While the chlorotic condition of the plants on the left is characteristic of 
the lack of manganese, this condition was expected to occur at a much 
earlier time in the growth, unless the plants received manganese from 
the pot. 
To prove that the pot was a source of manganese, new pots were 
made of acid-proof stoneware and the experiment with tomato plants 
was repeated. The result is shown in B. 
The difference in the growth of the tomato plants in the pots on the 
left in B and C is due to the fact that the pot on the left in C contained 
manganese absorbed in the walls of the pot, and this became available 
to the plants during the earlier part of their growth. Apparently the 
supply of manganese became exhausted a short time before this photo¬ 
graph was made, as is indicated by the fact that the branches and leaves 
became chlorotic and showed other signs characteristic of plants deprived 
of the amount of manganese necessary for their growth. 
The plants in the pot on the left in B illustrate the condition attained 
when manganese is entirely eliminated from a sand culture containing 
available compounds of lie 10 elements which have hitherto been 
regarded as all that are necessary for the growth of plants. The plants 
in the pot on the right in B grew in sand containing the same amounts 
of these compounds and enough manganese carbonate to supply about 
0.25 per cent of the element manganese, to the sand. The plants in 
the two pots are of the same age. 
From the facts here presented it seems evident that earthenware pots 
of the grade in common use in pot experiments may be sufficiently porous 
to absorb enough plant nutrients to affect the growth of other plants 
grown in the same pots at a later time. Acid-proof stoneware should 
be used in exact work. 
