84 BOTANICAL GAZETTE [FEBRUARY 
in good soil only partially yellow before they drop, while the leaves on 
plants in poor soil always completely yellow before dropping. This 
might suggest that mottling and dropping involve different factors. 
MEYER (38) points out that leaves of Tropaeolum passed 
through the following stages: dark green 25 days, green 6 days, 
bright green 12 days, yellow green-yellow 3 days, and then bright 
yellow. The young leaves at the top of the stem were dark green, 
while those at the bottom were yellow or wilting. The yellowing 
he believed to be due to the aging of the leaves. The change from 
bright green to yellow green was very rapid, and took place in 
much the same manner as that described for Coleus. 
MorPHOLOGICAL EXAMINATION 
In comparing microscopically the green with the mottling leaf, 
several striking differences were observed. In the green leaf the 
chloroplasts were large and blue-green, and one to three or more 
starch grains were clearly visible in the chloroplasts. The guard 
cells seemed to retain their coloring matter longer than the adjoining 
cells. In the mottled leaf the chloroplasts were yellowish, fewer 
in number, much smaller, without a green tint, and without starch 
grains. The chloroplasts were clustered about the apparently 
normal nuclei or distributed throughout other parts of the cells. 
Also the general appearance of bacteria being active here was 
observed, and will be discussed later. The chloroplasts in the 
palisade cells of the normal green leaves were 2-5 uw in diameter, 
while those in the mottled leaves were 1 wu or less in diameter. 
The chloroplasts in the guard cells of the green leaves, as well 
as those in the mottled leaves, were about 1 yw in diameter. 
Swart observed that in the aging of leaves the chloroplasts broke 
down and the starch disappeared, but the nuclei and the plasma 
layers remained. He was not certain whether the chlorophyll 
escaped from the cell or not. The chloroplasts of the deep green 
leaves of Tropaeolum majus, as noted by MEyeEr, were larger than 
those of the pale green leaves. Since he made some very accurate 
determinations of the sizes of the chloroplasts and correlated the 
size with the color of the leaves, it will not be out of place here 
to quote him rather fully. 
