43 
of pineapples in calcareous soils the plant is unable to form the chloro- 
phyll as fast as it is destroyed by the light. When the plant is 
partially shaded, however, the balance of the reaction is shifted; the 
chlorophyll is destroyed less rapidly, though it may be formed at the 
same rate as in the sunlight, so the plants become greener. 
The appearance of less chlorotic plants in shaded portions of a field 
affected with chlorosis is, then, due to the fact that the plants have 
made a less rapid growth at the start than the rest of the plants, and 
also to the fact that the chlorophyll is destroyed less rapidly in the 
shaded plants. 
CONCLUSIONS FROM INVESTIGATIONS OF THE CHLOROSIS. 
In deciding as to what is the primary cause of the failure of pine- 
apples on calcareous soils and of the appearance of the chlorosis, it 
should be borne in mind that chlorosis is not a specific disease, but is 
merely an outward manifestation that attends certain physiological 
disturbances in the plant. Plants suffering from poor drainage and 
from bacterial diseases and certain plants growing on calcareous soils 
all show chlorosis. It should also be taken into consideration that 
one disturbance in the physiology of the plant will bring on a series of 
other disturbances, which are to be regarded only as attendant 
phenomena. 
In the abdve investigations it was found that pineapples, in common 
with some other plants showing chlorosis on calcareous soils, were 
greatly benefited by treatment with iron salts, the iron salts over- 
coming the chlorosis and inducing a normal growth. 
No other treatment was found that overcame the chlorosis. It 
appears, then, that the plants need iron and that they are unable to 
obtain this from the soil, although there is a large percentage of iron 
in some of the calcareous soils. The facts that solutions of ferrous 
sulphate applied to the soil gave no result, while crystals applied to 
the roots or solutions of iron applied to the vegetative portions of the 
plant gave marked improvement as soon as they were absorbed, show 
that the carbonate of lime in the soil reacts with the iron (forming 
ferric carbonate) and depresses the availability of the iron for the pine- 
apple plant. That all species of plants growing on calcareous soils 
do not suffer to an equal degree for lack of iron is probably because of 
their different abilities to take up iron. That certain species of plants 
differ in their ability to take up phosphoric acid is well known. 
The ash analyses support in a general way the assumption that 
there is a lack of iron in the chlorotic plants and show that probably 
the increased absorption of lime creates a necessity for an increased 
quantity of iron. The excessive amount of lime in the plant may 
render inactive the small quantity of iron absorbed.t| With our pres- 

1 See also Hiltner, Loc. cit. 
[Bull. 11] 
