Aug. 15, 1921 
Effect of Ammonium Sulphate upon Plants 
707 
In the first experiment each culture solution of the two series used 
was supplied with 0.83 mgm. of iron per liter of nutrient solution in 
the form of an aqueous suspension of ferric phosphate. This amount 
of iron was added to each culture jar at the time the solutions were 
renewed. 
general appearance op the plants 
At the beginning of the third week of the growth period the plants in 
some of the cultures of the Tottingham series began to show the yellow 
appearance which is characteristic of plants suffering from lack of iron. 
This chlorotic condition later became general throughout the series. 
The yellowing of the leaves was usually more pronounced in the cultures 
having salt proportions which were unfavorable for good growth and 
in which the plants were smaller as a result of this unbalanced condition 
of the solutions. In general, however, there was good agreement in the 
appearance of the three plants in any one culture. That the chlorotic 
condition of the plants in this series was caused by the lack of available 
iron was made clear by the use of supplementary cultures to which iron 
in the form of ferrous sulphate was added in amounts equivalent to 
those contained in the ferric phosphate supplied to each culture. The 
chlorotic plants in these cultures invariably regained the normal green 
color of healthy plants in the course of a few days after the soluble iron 
was added. At the end of the growth period the plants in most of the 
cultures of the Tottingham series were very chlorotic and not nearly so 
large as were the plants in the corresponding cultures of the ammonium- 
sulphate series, these differences in size being paralleled by similar 
differences in the dry-weight yields, as an inspection of the data in Table 
III will show. The plants in the cultures of the ammonium-sulphate 
series, on the other hand, were very green; and in so far as could be 
judged from their general appearance they were vigorous and healthy, 
with the exception of the plants in several cultures which were not quite 
so green in color but otherwise appeared to be in good condition. The 
slight yellowness in the plants of these few cultures was of a different 
nature from that which occurred in the plants of the Tottingham series. 
There were, of course, large differences in the size of the plants of the 
different cultures resulting from the differences in salt proportions 
throughout the series. There was, however, no evidence of the lack 
of chlorophyll in the leaves, such as characterized the plants of the 
Tottingham series. 
INFLUENCE OF THE GROWING PLANTS ON THE HYDROGEN-ION 
CONCENTRATION OF THE SOLUTIONS 
It is, of course, well known that plants tend to change the reaction of 
culture solutions in which they are grown. A large number of supple¬ 
mentary tests made in connection with this work have brought out the 
fact that the rate of this change in a culture solution is dependent upon 
a number of different factors, some of the more important of which are 
