TRANSACTIONS OF THE SECTIONS. 145 
manner as if placed on the natural stigmatic surface, instituted a num- 
ber of experiments, of which the following are the general results :— 
1. The spores of cryptogamic vegetables, which some botanists consider 
analogous to pollen, do not dehisce under the influence of acids. 2. 
The pollen of the Grasses is spherical, both when dry and placed in 
water ; with acids it bursts, protruding one long cylindrical mass, which 
remains afterwards unacted upon by the liquid. 3. The pollen of the 
Aroidez, Colchicacese, Smilacez, Liliacee, Commelinacez, Buto- 
mace, Amaryllidacez, Iridaceee, and Canne, are, when dry, oval, 
and marked with a dark neutral 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 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 alteration in its form, after which the endopollen 
remains unacted upon by the liquid. 4. In the Salicinez, Salicarie, 
Leguminose, Rosacewx, Crassulacez, Saxifragaceze, Hypericacee, Ruta- 
cee, Hippocastanee, Resedacee, and the tribe Helleborez of the 
Ranunculacez, the pollen when dry, oval, and marked with a dark 
central line, becomes, when placed in water, round, or nearly so, the 
dark line disappearing ; and when acted upon by acids, assumes a 
triangular form, and protrudes at three equidistant points cylindrical 
or club-shaped masses, very similar at their origin to tubes, and pre- 
senting the appearance of being enveloped 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 
Ericacez and Epacridacee, the pollen grains, when dry, appear trian- 
gular or oval in some instances, triangular or rhombic in others, 
according to the position in which they are examined. Having ascer- 
tained the results of acids on the pollen, the author was induced to 
examine the stigma, and in every case found that the stigmatic tissue 
gave indications of an acid re-action upon litmus paper. The next 
question to be examined was, in what manner is the fertilizing influ- 
ence of the male organs communicated to the ovule? After quoting 
the opinions of Amici, Brown, Fritzche, Corda, Treviranus, Brongniart 
and others, the author came to the conclusion that the boyau, or 
‘intestine-like protrusion from the pollen grains, was the result of the 
action of acids upon the fluid which contained the fovilla in the pollen 
grain ; and he inferred this from the fact of this tube, or boyau, never 
being formed when the pollen grain is placed in water, but being 
constant when the grain is placed in acid. After describing and ex- 
plaining the anomalous character of the pollen grains in Orchidacez, 
Fumariacee, Asclepias, &c., the author presented the following con- 
clusions 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 coagu- 
lated, enveloping the fovilla, and assuming, according to the method 
of dehiscence, different and very remarkable forms. ‘The memoir was 
illustrated by an extensive series of drawings. 
1840. L 
