Ig09] BRIEFER ARTICLES 227 
cause of which I have not investigated. Also, Tropaeolum leaves soon 
turn yellow in darkness. The second injurious result, and the most impor- 
tant in this study, occurs in nearly all plants. Some of the photosynthate 
is of course being constantly used in growth or for storage in the stem, and 
since the plant can make no more in darkness, the percentage of sugar in 
the cell-sap decreases more and more by diffusion into the stem. Then, 
as PFEFFER has shown,3 when the plant is brought into the light no starch 
is deposited until this percentage of sugar is repaired. The following 
example is typical: Two plants of Fuchsia speciosa, apparently alike, were 
put in the light at the same time, after having been in darkness, the one 
64 hours, the other 16 hours. Halves of leaves tested showed no starch. 
After 2 hours in the light, the other halves on the first plant showed much 
less starch than those on the second plant. To obtain the most rapid 
formation of starch, therefore, it is important that the plant should be kept 
in darkness only long enough just to cause the disappearance of starch. 
The disappearance of starch is not always even. In Coleus, Primula 
verticillata, Primula obconica, and Fuchsia speciosa, the base of the leaf is 
emptied of starch before the tip. This agrees with what SacHs found in 
Some other leaves.4 So far as I have tested them, I have found this to be 
true only of ovate or oblong leaves. This may be correlated with the greater 
abundance of stomata near the base of the leaf. _In round leaves like Pelar- 
gonium zonale and Tropaeolum, the starch seems to disappear evenly from 
all parts. The starch disappears from the young leaves on a plant before 
It does from those which are mature. 
The effects of temperature on the amount of starch present are especially 
important. In several of my experiments, leaves of Fuchsia spectosa, 
Euphorbia pulcherrima, and Pelargonium zonale which were kept in direct 
sunlight 4 hours showed very little starch, while leaves on plants in diffuse 
light, at the end of 4 hours were full of starch. Fuchsia speciosa after being 
in diffuse light at 28°-31° C. for 3 hours showed only a trace of starch, while 
other leaves in 3 hours at 18°-20° C. appeared black with starch, with the 
lodin test. A comparison of these two sets of experiments shows that the 
small amount of starch present in leaves in direct sunlight isund btedly con 
hected with their high temperature. In order to get the best results, there- 
fore, from experiments in the formation of starch in the leaves of potted 
steenhouse plants, it is necessary to keep the plants at a temperature not 
exceeding 22° C., and to insure this it is well to keep them in diffuse rather 
than in direct sunlight. It will be of interest to compare these results with 
those obtained by Sacus for outdoor plants, as described in his classical 
3 Physiology 1: 321. 4 Ges. Abhandl. 360. 
