Notes. 
273 
and also attempted to determine the total amount of starch formed 
or dissolved in a given time by observing the variation in weight 
of equal areas of the leaf-lamina cut from the two sides of a large 
leaf like that of the Sun-flower. As these variations in weight of 
the dry leaf were found to be correlative with the indications of 
the iodine-test, they were attributed to a loss or gain of starch. 
An examination of the method proves, however, that it cannot 
give us the actual amount of starch formed or lost within a given 
period, but that it really measures the total assimilated products which 
have entered or left the leaf. Sachs speaks of it throughout his 1884 
paper as a gain or loss of starch , because he assumes (although he 
nowhere precisely states it in this form) that all the products of 
assimilation pass at one time of their history through the form of 
starch in the chloroplasts. We have, however, no proof that starch 
is an essential link in the chain of chemical products, beginning with 
the inorganic materials and ending with the form in which the 
products leave the leaf. That a large part of the first products of 
assimilation does pass through the starch-stage under ordinary 
conditions there can be no doubt, especially when assimilation i9 
very active; but no sufficient experimental proof, or in fact proof 
of any kind, has been given of that constant and rapid flux of starch 
within the chlorophyll-corpuscle which must go on if this assumption 
of Sachs is correct. Our own work is strongly opposed to this 
assumption, and points to by far the larger amount of assimilated 
material never passing through the stage of starch at all. 
The half-leaf gravimetric method of Sachs is nevertheless a very 
valuable one if we bear in mind its limitations, and it gives us 
a very good idea of the amount of material assimilated in a given 
time by a given area of leaf. 
In the full paper 1 we have given the results of a considerable 
number of determinations by this process, and have also determined 
the limits of error of the method. Our results agree very closely 
with those of Sachs in showing that the leaves of the Sun-flower, 
for instance, can, under favourable conditions, assimilate at the rate 
of from i-o to 1-5 grams per square metre of leaf-area per hour. 
We have been able to show however that only a small portion of 
this assimilated material exists at any one time in the form of starch . 
1 Journal of the Chemical Society, vols. Ixiii, and lxiv, No. 366, May 1893. 
