216 ON POLLEN AND VEGETABLE IMPREGNATION. 
ART. XLI. — ON POLLEN AND VEGETABLE IMPREGNATION. 
[A memoir on this subject was read before the British As- 
sociation, for the advancementof science, by Dr. Aldridge of 
Dublin, detailing the results of observations he had made re- 
specting it, which appear to us novel and interesting. The 
following is the substance of the memoir — A. S.} 
Dr. Aldridge having discovered that nitric and other inor- 
ganic acids, produced the dehiscence of the pollen-grains, in 
the same manner as if they were placed on the natural stigma- 
tic surface, instituted a number of experiments upon this sub- 
ject. His results are: 
1. The spores of cryptogamic vegetables, which some bo- 
tanists consider analogous to pollen, do not dehisce under the 
influence of acids. 
2. The pollen of the grapes is spherical, both when dry and 
placed in water ; with acids it bursts, protruding in one long 
cylindrical mass, which remains afterward unacted upon by 
the liquid. 
3. The pollen of the Adroidese, Colchicaceae, Smilaceae, 
Liliaceae,Commelinace3e, Butomaceae, Amaryllidaceae, Iridaceae 
and Cannae, are, when dry, oval, and marked with a dry neu- 
tral line, but become, when placed in water, more broadly 
oval or circular, the long diameter remaining the same, and 
the opake line disappearing ; after the addition of an acid the 
external membrane of the pollen, or peripollen, dehisces by a 
chink or suture, sufficiently broad to permit the contents or 
endopollen to escape without any change of form, after which 
the endopollen remains unacted upon by the liquid. 
4. In the Salicineae, Salicariae, Leguminoseae, Rosacea?, Cras- 
sulaceae, Saxifragiae, Hypericaceae, Rutaeeae, Hypocastaniae, 
Resedacese, and the tribe Helleboreas, of the Ranunculaceae, 
the pollen when dry, oval, and marked with a dark central 
line, becomes, when placed in water, round, or nearly so — the 
