Remarks on tie Impregnation of Plants. 311 
ial and some other plants, the cavity of which he erroneously 
considered to lead directly into the seed-vessel. ‘This cavity, how- 
ever, only exists in some compound styles, being formed by the co- 
hesion of three or more simple styles so as to form a hollow cylinder, 
and it consequently does not communicate with the interior of the 
ovary. Moreland also observed the micropyle (the vestige of the 
foramen of the ovule) in peas and beans; he supposed it to be a 
perforation produced by the entrance of a grain of pollen, which, 
having fallen down the tube into the ovary, had at length ente 
the ovule and become the embryo or seminal plant. 
It was discovered, I think by Needham, that when grains of pollen 
are moistened or thrown upon water, they usually burst with vio- 
lence and discharge the slightly viscous and turbid fluid contained 
within. To this fluid the immediate agency in impregnation was 
attributed by Linneus and contemporary botanists. ‘Two opinions, 
however, have prevailed respecting the mode of its action upon the 
ovule ; some writers supposing the fluid itself to be conveyed down 
the diyte to that organ, while others conceived that a peculiar action 
excited upon the stigma was transmitted to the ovule by a kind of 
oe The former view appears to have been adopted by Lin- 
eus.* The latter was sustained by Grew and several succeeding 
plicit. Our actual knowledge upon this subject was, how- 
ever, confined to the simple fact that the application of the 
to the stigma was essential to the fertilization of the ovules, all the 
information we possess respecting the action of the pollen after it 
has reached the stigma being of very recent date. The earliest of 
aseries of highly curious discoveries on this hitherto mysterious 
subject was announced in the year 1823. A few remarks on the 
structure of pollen will form a necessary introduction to our account 
of these interesting researches. 
The pollen, when examined by a moderate magnifying power, is 
seen to consist of a multitude of grains of some regular form, which 
is uniform in the same species, but often differing widely in different 
plants. It has been satisfactorily proved that these grains are com=- 
posed of two coats, of which the exterior is rather thick and nearly 
inelastic, while the inner is an exceedingly delicate and highly ex- 
* Generationem vegetabilium fieri mediante pollinis antherarum illapsu sup: 
Stigmata nuda, quo rumpitur pollen efflatque awrem ‘seminalem, que Ne 
ab humore stigmatis, &c.—Linn. Phil. Bot. ed Stockholm. 1751. p.91. 
