ON POLLEN AND VEGETABLE IMPREGNATION. 217 
dark line disappearing; and when acted upon by acids, as- 
sumes a triangular form, and protrudes at three equidistant 
points cylindrical or club-shaped masses, very similar at their 
origin to tubes, and presenting the appearance of being en- 
veloped by a membrane. 
5. In the greater number of the remaining dicotyledons 
examined, the dry pollen is opake, and either broadly oval or 
spherical. 
6. In the Ericaceae, and Epocridaceae, the poHen grains, 
when dry, appear triangular or oval in some instances, trian- 
gular or rhombic in others, according to the position in which 
they are examined. Having ascertained the results of acid 
on the pollen, the author was induced to examine the stig- 
ma, and in every case found that the stigmatic tissue gave 
indications of an acid reaction upon litmus paper. The next 
question to be examined was, in what manner the fertilizing 
influence of the male organs is communicated to the ovule? Af- 
ter quoting the opinions of Amici, Brown, Tritzche, Corda, 
Treviranus, Brongniart and others, the author came to the 
conclusion that the bogan or intestine-like protrusion from 
the pollen grains is the result of the action of acids upon the 
fluid which contains the fovilla in the pollen grain ; and he 
infers this from the fact of this tube or bogan never being 
formed when the pollen grain is placed in water, but being 
constant when the grain is placed in acid. After describing 
and explaining the anomalous character of the pollen grains 
in the Orchidaceae, Fumaraceae, &c, the author presents the 
following conclusions as the result of his researches: 1. The 
stigma is invariably acid. 2. It is in consequence of this 
acidity, that the pollen bursts. 3. That by the same means 
the fluid contents of the pollen become coagulated, enveloping 
the fovilla, and assuming, according to the method of de- 
hiscence, different, and very remarkable forms. 
VOL. VII. — NO. III. 
28 
