22 
The Colorado Experiment Station 
its power of absorbing moisture from the plant. Iron sulphate 
appears, in addition to this action, to produce a chemical effect 
upon the dandelion leaves whereby they turn black. The most 
pronounced effect appears to be due to the action of the chemical 
upon the green coloring miatter ( chlorophyll ) of the leaf, where¬ 
by it is partly decomposed, a dark-colored material being left in 
the leaf as the result. It was noted that the application of the 
iron sulphate to dandelion foliage caused the milk or latex in the 
leaves and flower stalks to ooze out in drops, sometimes of con¬ 
siderable size, within half an hour. 
This phenomenon, while offering an 
interesting subject for study, has not 
been investigated sufficiently by the 
writer for an explanation. It appears 
to be due to the absorption of the iron 
salt by the cells of the leaves and 
flower stalks and the production of 
sufficient internal pressure (turgor) to 
rupture the cell walls and liberate the 
latex. It is possible, moreover, that a 
corrosive action upon the tissues of 
the leaf takes place which weakens or 
partly destroyes the cell walls which 
confine the latex of the plant. The 
effect is most rapid in warm weather 
when the spray becomes concentrated 
upon the surface of the plants by evap¬ 
oration of the moisture and when the 
plants are full of the milky juice. 
Blackening and withering.of the dandelion foliage, due to appli¬ 
cations of iron sulphate, are hastened by direct sunlight. This 
was shown by densely shading a portion of a treated plant for 
three days. At the end of 9 hours the plants exposed to direct 
sunshine were blackened, while the shaded ones were only slightly 
discolored. At the end of three days, however, there was practically 
no difference in the blackening of the shaded and unshaded plants. 
In order to secure the maximum effects of the iron sulphate 
spray, it is desirable to apply it during comparatively dry weather, 
altho in some of our experimental work a light shower a few 
hours after the application did not appear to decrease its effect¬ 
iveness. It is advisable, however, that no irrigation be given the 
lawn within less than 24 or 36 hours after the spray is applied dur¬ 
ing clear weather ^nd during cloudy weather this time should be 
Fig 1 . 11. Flower heads from 
which the ripening seeds have 
been removed and eaten by 
birds. 
