274 
Notes. 
It is evident that if we are to get at any of the metabolic secrets 
of the leaf an accurate method of starch-determination is, at the 
outset, essential, since no reliance can be placed upon any of the 
iodine-tests except for very rough relative estimates. 
We have found it possible to estimate the starch of leaves with 
great exactness by hydrolyzing it, with suitable precautions, with 
diastase, and then determining the products of hydrolysis in the 
usual way by means of the polarimeter and Fehling’s solution. It 
will not be necessary to enter here into the details of this process, 
but we will give the results of two such determinations of starch 
in the same leaf, in order to show how concordant the results are. 
In two analyses of the same sample of dried Tropaeolum - leaf we 
found:— 
(1) 6- 40 per cent, starch. 
( 2 ) 6.54 „ „ 
As a square metre of dry TropaeolumA^i weighs about 25 grams 
these amounts represent per square metre of leaf about i-6 grams 
of starch. 
Precautions have to be taken in drying the leaves for these 
determinations, for if the leaf is dried too slowly and at too low 
a temperature there is a considerable loss of starch during the 
process owing to certain functions of the living cells, especially the 
respiratory processes, continuing for some time. The leaves must 
be killed rapidly by a fairly high temperature, or better still, can 
be submitted for a short time to chloroform-vapour, after which they 
may be dried at from 30° to 40°. 
In order to give an idea of the fluctuations in the amount of starch 
when the leaves are placed under various conditions, we give the 
results of a few determinations made on Tropaeolum-Xzmz.s : — 
Starch 
Grams of Starch 
per cent. 
per scp m. 
(1) Leaves plucked at 5 p.m. on a ) 
sunny day / 
6-50 
1-756 
(2) Same leaves depleted in dark | 
for 63 hours J 
2-05 
o-554 
Another similar experiment. 
(1) Leaves plucked in afternoon 
5'42 
1-464 
(2) Leaves in dark for 60 hours 
0-90 
0-244 
On determining the total amount of matter assimilated by a square 
