30 The Batanical Gazette. [January, 
Kreusler* has shown the great influence of the amount of 
water contained in leaves on their assimilative activity. 
‘‘While a complete saturation of the atmosphere does not in 
itself seem unfavorable to assimilation, the latter may, on the 
other hand, be considerably reduced by a dry atmosphere and 
the subsequent powerful evaporation, long before the leaf 
loses visibly in turgescence. Although it is well known that 
starch does not represent the primary product of assimila- 
tion® still its presence or absence may be used as a good com- 
parative test. It was found that in thase plants which can 
not close their stomata even after they are quite withered 
starch was made, viz., in Rumex aquaticus, Caltha palus- 
tris, Hydrangea hortensts, and Calla palustris. On the other 
hand leaves with closed stomata made no starch. If the sto- 
mata on a turgid leaf are closed with a mixture of one part 
bleached bees-wax and three parts of cocoa butter (this mix- 
ture is perfectly harmless to the leaf, does not melt below 40° 
C. and is easily washed off with water) no starch will be found. 
If the upper and not the under side is coated there will be no 
noticeable decrease in the amount of starch formed. The au-_ 
thor concludes that under ordinary conditions the main gas 
exchange is through the stomata and that through the cuti¢- 
ularized epidermis is very small incomparison. This is true 
even in very young leaves. When the cuticularized surface 
is scratched or cut, allowing the entrance of CO,, starch will 
be formed by the cells receiving CO, through the wound. 
When the air around the leaves contains about 5 per cent: 
CO, a sufficient amount passes through the cuticularized walls 
to make a large amount of starch. 
Ill. Prejudicial effect of an increased amount of salt in the 
substratum on assimilation. 
th 
mung agebl 
der Naturforscher-Versammlung zu Strassburg 1885: ; ; 
*Brown & Morris, A contribution to the cdasnabitey cua physiology of folis#? 
leaves. Jour. Chem. Soc. Transactions London 63: . . : 
*°Schimper, A. F. W., Botanische Mittheilungen aus den Trope?. im” 
Indo-Malayische Strandflora. Heft 3. 1891. 
q 
i 
