Remarks on the Impregnation of Plants. 311 



perial 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 entered 

 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 Linnaeus 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 style to that organ, while others conceived that a pecuhar action 

 excited upon the stigma was transmitted to the ovule by a kind of 

 sympathy. The former view appears to have been adopted by Lin- 

 naeus.* The latter was sustained by Grew and several succeeding 

 philosophers. Our actual knowledge upon this subject was, how- 

 ever, confined to the simple fact that the application of the pollen 

 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 

 a series 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 supra 

 stigmata nuda, quo rumpitur pollen efflatque aurem seminalem, quae absorbetur 

 ab humore stigmatis, &c.—Linn. Phil. Bot. ed Stockholm. 1751. p. 91. 



