BRIEFER ARTICLES 
ON THE DEMONSTRATION OF THE FORMATION OF 
STARCH IN LEAVES 
For a qualitative demonstration of photosynthesis in starch-forming © 
leaves it is advantageous to know the time in darkness required for the 
disappearance of accumulated starch, and the time in light required for its 
subsequent demonstrable formation. No general rule can be given for 
either, since the time required varies widely for the different species. 
Therefore, in continuation of the series of studies carried on in the labora- 
tory of plant physiology of Smith College on the physiological constants 
of the educationally useful plants,t I have tried to determine these data for 
such plants, and also, by comparison, the best plants for the purpost- 
Throughout this paper I have used the expression “disappearance of 
starch” rather than ‘“‘translocation.” In a general way the processes, of 
course, correspond, yet the term “translocation” implies the removal 0: 
the starch from the leaf, while here we are dealing only with its disappe*™ 
ance as starch. : 
The method employed in the present study was as follows: Five actively 
growing plants of each species, always after a bright day and between 4 2 
5 o’clock, were put in a dark room having a steady temperature of 18°-22° C. 
as recorded by a thermograph. Twice a day, about 9 A. M. and 2 P. M., 
leaves were tested for starch by SAcHs’s iodine method, and the time when 
all starch had disappeared was noted. No attempt was made to find the 
exact hour when the leaves were empty. This would necessitate testing 
them every hour during the night as well as during the day, 
purpose of the present study, the results would be of little value- 
following table, therefore, the time in darkness required to empty the 
of starch is given in night and day periods rather than in hours. 
iodin test the leaves were first boiled 1 minute to swell the starch, 
blanched in warm alcohol, were put in water a few minutes to remove of 
alcohol and soften the tissues, and were then immersed in 4 solution 0 
iodin. The solution used was git potassium iodid, 1°™ iodin, 10% watel, 
to which, when dissolved, water was added to make 1 liter of solution. fie 
Thus was the time of disappearance of starch determined with su 
cient accuracy for all practical purposes. To determine the time Ted" 
‘Bor. GAazETTE 40:302. 1905; 45350. 1908; 482254. 1908; 465° 1968 
46:221. 1908. 
Botanical Gazette, vol. 48] 
leaves 
or the 
were 
the 
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