LIFE OF PLANTS. 



253 



tion, and still farther by the difference in the number and in- 

 sertion of the unimpregnated ovula, from that of the impreg- 

 nated seeds, and by the constant failure of the former, when 

 they are not awakened by the pollen into new life. 



We might indeed suppose, with the natural historians of 

 the early part of the eighteenth century, that there is a direct 

 passage of the pollen into the ovary, and a material union of 

 this substance with the ovula ; by which supposition, w e 

 should explain the germination of the seed entirely on atomi- 

 cal principles, (Sam. Moreland, Phil. Trans, vol. xxiii.) ; but 

 the following reasons lead us to reject this supposed direct 

 passage. In the first place, there are no visible canals through 

 which this passage could take place, except the sap-vessels 

 of the pistillum and the spiral vessels, both of which connect 

 the germen with the stigma. But sap-vessels and spiral ves- 

 sels perform quite different functions, as we have already 

 seen. 



In the next place, the surface of stigmata, as we have al-* 

 ready remarked (340.) is covered with shut warts and hairs, 

 which equally prevent this direct communication. 



It must also be noticed, that in the Labiatae, Asperifoliae^ 

 some of Urticae, and Rosaceae, the pistillum only directs itself 

 sideways towards the ovula, without appearing to stand in di- 

 rect communication with them ; and that in the Contortas the" 

 pistilla are covered by a shield-shaped surface resembling the 

 stigma, without being directly united to it. Finally, w^e must 

 allow its privilege to analogy, which informs us, that in the 

 lower animals, particularly in the Molluscas, impregnation is 

 accomplished without the passage of any material substance 

 from the impregnating organ into the receptacle of the seed. 

 In this case it is purely a galvanic process, in which, by 

 means of a chain of different organs lying together, the vital 

 activity is unfolded to the degree necessary for the production 

 of new individuals. A process exactly similar takes place in 

 the vegetable kingdom. The pollen, brought into contact 

 with the stigma, awakens in it, as well as in the germen, a 

 new Hfe. New secretions and depositions of organising mat- 

 ters take place, by means of which new forms are produced 



