282 BOTANICAL GAZETTE [Marco 
controlled conditions, Knicut’ has performed experiments with various plants 
with results which show no close agreement between stomatal opening and rate 
of transpiration, but which tend to demonstrate that the water content of the 
leaf is an important factor in controlling its water loss by transpiration, and 
further that stomatal aperture is not reduced by slight water deficiency in the 
leaf, but is very sensitive to light changes. On the whole, his results support 
Livrncston’s contention of the regulatory importance of “incipient wilting,” 
and are directly opposed to DARWIN’s theory that stomatal aperture plays the 
primary réle in the regulation of transpiration. 
Working with detatched leaves and with potted plants, Martrn® has con- 
firmed previous conclusions in finding that films of Bordeaux mixture cause 
decided acceleration in the rates of transpiration, and that their influence is 
apparent as soon as the spray dries upon the leaves. More recently results 
of the same nature were obtained by Suive and Martin, using cobalt chloride 
paper. The indices of the transpiring power of the sprayed leaves are shown 
to be rather more than 20 per cent higher than for the untreated leaves of the 
same plant. It is also interesting to note that the investigators express their 
confidence in the accuracy of the results obtained by the cobalt chloride 
method, which may now be regarded as a reliable mantis especially adapted 
to field use. 
Not only are fungicides instrumental in era transpiration, but the 
fungi themselves may also act in a similar manner, as has been shown by 
WEAVER" for cereal rusts. Here the increase in transpiration occurs about the 
time the pustules break through the epidermis, and the amount of increase is 
closely related to the pustular area. 
Experimenting upon the relations expressed in the comparison of the 
relative water loss from the plant and the atmometer, termed by LivINGSTON 
“relative transpiration,” Knicur™ finds that this does eliminate the influence 
of changes of temperature and relative humidity on rate of transpiration. He 
asserts, however, that “relative transpiration” does not necessarily represent 
changes in the intrinsic transpiring power of a plant unless conditions of air 
movement are constant. This is because of the unequal response of plant and 
atmometer to changes in wind velocity —Gro. D. FULLER. 
7 Knicut, R. C., The interrelations of stomatal aperture, leaf water-content, and 
transpiration rate. Aas. Botany 31:221-240. 1917. 
* MaRtiN, W. H., ermine ot Bordeaux sage on the rates of transpiration 
t r. Agric. Research 7:529-548. 1916. 
9 Suive, J. W., and Mins. Ww. , ae ao of surface films of Bordeaux 
aikbie on oe folie transpiring power in tomato plants. Plant World 20:67-86. 
TgI7. 
© WeavER, J. E., The effect of certain rusts upon the transpiration of their hosts. 
Minn. Bot. Studies 4:379-406. 1916. 
™ Knicat, R. C., “Relative transpiration” as a measure of the intrinsic transpit- 
ing power of the plant. Ann. Botany 31:351-360. 1917. 
