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POPULAR SCIENCE REVIEW. 
black being 100. To measure the absorbent power, a thermopile was 
formed of a thin sheet of copper riveted to a steel spring. One face was 
covered with lampblack, the other with the leaf to be examined. Ex- 
posing the two surfaces in turn to the radiation of a metallic blackened box 
heated by steam, and waiting until the galvanometer needle came to rest, 
the ratio of the deviations gave the absorbent power of the leaf. From the 
results it appeared that the absorbent power is sensibly equal to the emissive 
power, and consequently the amount of dew deposited on plants should be 
determined by pluviometers painted black. 
The Functions of the Stomata in Plants. — This subject has been recently 
investigated by Mr. T. Meehan, who has presented a paper on it to the 
Academy of Sciences of Philadelphia. From this it seems that the current 
ideas as to the functions of those structures are somewhat erroneous. Mr. 
Meehan exhibited a leaf taken from a small tree of Acer jiseudo-platanus 
— the common sycamore maple — which had assumed an inverted position. 
The tree was three years old from seed, and all the leaves were of that 
character. The young leaves first appeared in their normal condition, 
but as the petiole lengthened, the leaf blade bent under, so that the 
under surface was exposed to the full sunlight, and under the petiole 
above. He also exhibited a young oak from an acorn sown in the 
spring, and which he believed to be Quercus Catesbeei , and in which all 
the leaves were vertical, and not with their surfaces on a plane with the 
horizon, as is the case with all other seeding oaks and American trees. He 
said it was possible this position of the leaves was not continued with the 
increased age of the tree, or it would have been observed and placed on 
record. Of several hundred young plants, all had the same character. The 
facts were simple in themselves, but had great interest to the student in 
vegetable physiology. The stomata were usually on the under side of the 
leaf, and believed to be there of a necessity. Our leading botanical text- 
book taught that stomata were breathing pores, and could not carry on their 
essential operations when exposed to direct sunlight ; and the same high 
authority had suggested that if leaves of this character could be inverted, 
and forced to remain in this condition, the plant would inevitably die. 
The maple did not die, but had been during all its existence as healthy as 
others of the same species growing near it. A large number of the pro- 
teaceous and myrtaceous plants of South Africa and Australia, and of which 
the now famous Eucalyptus globulus is a familiar example, had their leaves 
vertical, as in this oak. This had been accounted for by the statement that 
these leaves had stomata on both surfaces of the leaf, and the effort of these 
stomata to face the earth had of course resulted in an even balance of power, 
in which neither side had any advantage. The stomata on each side of the 
leaf had to face the horizon. Supposing this might account for the position 
of these oak leaves, they, as well as the maple, had been examined micro- 
scopically by Dr. Hunt, of the Academy, and found to have stomata only on 
one — the normal side. He thought it safe to conclude, from these facts, 
that the accepted theories of the relation of stomata to light required some 
modification. 
j Extraordinary Growth of Vallisneria spiralis. — Mr. A. W. Bennett, 
M.A.,B.Sc., asks the editor of the u Journal of Botany”: Can any of the 
