542 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9. 
have shown that the chlorophyll content of leaves of certain species in- 
creases until the leaf is mature, after which it decreases. Possibly the 
decrease in chlorophyll may be attributed to the breaking down of the 
proteins of the chloroplasts, due to a shortage of carbohydrates in the plant 
and their use as a source of this material (Meyer, 1918), or to a shortage of 
nitrogen (Schertz, 191 9). Palladin (1891) has shown definitely that a 
supply of soluble carbohydrates is necessary for the formation of chlorophyll, 
and it was thought that, aside from the age factor, the presence and dropping 
of the cotyledons might be involved. Their loss might mark a point of 
change in the chlorophyll content of the primordial leaves, caused possibly 
by the decreased supply of nitrogen or of carbohydrates or of both. Such 
changes might, it was thought, be great enough to overshadow or counter- 
balance any effect of spraying, although the possibility remained that they 
would emphasize it. Their importance in the growth of Phaseolus vulgaris 
is shown by the work of Liipke (1888), and in the growth of the Canada 
field pea by Duggar (1919), who assumes that they may be a source of 
organic nitrogenous material or of a vitamine. 
The chlorophyll content of the primordial leaves was determined at the 
following four stages of development: "Age ^4," immediately after the 
primordial leaves had unfolded; ''Age when the cotyledons were being 
shed, three days after "Age^"; "Age C," four days after "Age when 
the primordial leaves had attained a considerable size, but while their area 
still constituted the greater part of the photosynthetic surface of the plant; 
and "Age D," when the primordial leaves constituted only a small part of 
the total leaf surface but before they showed yellowing. Seventeen days 
elapsed between "Age C" and "Age D." 
The data for "Age A'' were obtained by measuring and weighing the 
primordial leaves of thirty-two plants; the primordial leaves from twenty 
plants were used to obtain the data for "Age ^ " ; those from sixteen plants 
for "Age C"; and those from twenty plants for "Age D.'' The results 
are shown in table i. ■ ■■ - .^ 
Table i . Chlorophyll Content of Primordial Leaves at Various Ages 
Age 
Area Both Primordial Leaves 
Fresh Wt. 
Leaf per sq. 
cm. (g.) 
wt. Chlorophyll (mg.) 
Sq. cm. 
% Increase 
Per sq. cm. 
Per g. Fresh Wt. 
''A " 
234 
.0241 
•0305 
1.26 
64.6 
176. 
.0186 
.0412 
2.22 
"C" 
107.8 
67. 
.0201 
■0395 
1.96 
146.0 
35- 
.0219 
.0388 
1.77 
During the period of growth before the cotyledons were shed, which 
was also the period of most rapid expansion, there was a marked increase 
in the amount of chlorophyll to the square centimenter. The increase to 
