VARIATIONS IN THE OSMOTIC CONCENTRATION OF THE 
GUARD CELLS DURING THE OPENING AND 
CLOSING OF STOMATA 
R. G. WiGGANS 
(Received for publication July 12, 1920) 
It has been repeatedly shown that the opening and closing of stomata 
are closely related to the turgor of the guard cells. The first critical study 
upon this point was made by von Mohl (1856). Following von Mohl, work 
has been done by Schwendener (1881), Kohl (1886), Francis Darwin (1898), 
Leitgeb (1886), and Lloyd (1908). These investigators state that the 
opening and closing of the stomata are due to variations in the turgor of the 
guard cells, and that the condition of the turgor of these cells depends, 
first, upon the abundance of water in the plant, and second, upon the amount 
of effective osmotic substances in the cells. It was supposed until recent 
researches that whenever a plant was not well supplied with water, or in 
other words in a slightly wilted condition, the stomata would always be 
closed. Many of the earlier investigators showed to their own satisfaction 
that whenever the plant begins to wilt the stomata invariably close. In 
more recent years, Laidlow and Knight (1916) and Lloyd (1912, 1913) 
have contradicted this statement after finding stomata still open when 
plants had become badly wilted. 
The second factor upon which the turgor of the guard cells depends, that 
of the amount of effective osmotic substances, has not been given so much 
attention. The observations made by Lloyd (1908) and Darwin (1898) on 
the starch content of the guard cells as compared with the other tissues 
of the leaves, and those made later by Iljin (1914), are the most important. 
Lloyd found that the starch content in the guard cells is greatest in the early 
hours of the morning and gradually disappears until the time when the 
stomata are at their maximum width. After the stomata begin to close 
there is a gradual accumulation of starch until the maximum is again 
reached at some hour during the night. Lloyd also found that the fluctua- 
tion of the amount of starch within the plastids of the guard cells is accom- 
panied by a complementary fluctuation of the oil content. 
Iljin (1914) made similar observations on the starch content of the guard 
cells of several plants which he had under study. The important phase of 
his work, however, was the actual determination of the differences in osmotic 
concentration between the guard cells of the stomata and the cells of the 
other tissues of the leaf. For the purpose of determining the threshold 
concentration, he used concentrations of KNO?, varying in strength from 
0.125 to 3.00 normal. His experiments in general showed an extra- 
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