Chap. XXVII. OF PANGENESIS. 375 



two forms, and the offspring from two birds with differently 

 coloured tails have their tails affected. 



The various tissues of the body plainly show, as many phy- 

 siologists have insisted,*^ an affinity for special organic sub- 

 stances, whether natural or foreign to the body. "We see this 

 in the cells of the kidneys attracting urea from the blood ; in 

 curare affecting certain nerves ; Lytta vesicatoria the kidneys ; 

 and the poisonous matter of various diseases, as small-pox, 

 scarlet-fever, hooping-cough, glanders, and hydrophobia, 

 affecting certain definite parts of the body. 



It has also been assumed that the development of each 

 gemmule depends on its union with another cell or unit 

 which has just commenced its development, and which pre- 

 cedes it in due order of growth. That the formative matter 

 within the pollen of plants, which by our hypothesis consists of 

 gemmules, can unite with and modify the partially developed 

 cells of the mother-plant, we have clearly seen in the section 

 devoted to this subject. As the tissues of plants are formed, as 

 far as is known, only by the proliferation of pre-existing cells, 

 we must conclude that the gemmules derived from the 

 foreign pollen do not become developed into new and separate 

 cells, but penetrate and modify the nascent cells of the mother- 

 plant. This process may be compared with what takes place 

 in the act of ordinary fertilisation, during which the contents 

 of the pollen-tubes penetrate the closed embryonic sac 

 within the ovule, and determine the development of the 

 embryo. According to this view, the cells of the mother- 

 plant may almost literally be said to be fertilised by the 

 gemmules derived from the foreign pollen. In this case and 

 in all others the proper gemmules must combine in due order 

 with pre-existing nascent cells, owing to their elective affi- 

 nities. A slight difference in nature between the gemmules 

 and the nascent cells would be far from interfering with 

 their mutual union and development, for we well know in 

 the case of ordinary reproduction that such slight differentia- 



*3 Paget, ' Lectures on Pathology,' Tissus Vivants,' pp. 177, 210, 337; 



p. 27 ; Virchow, ' Cellular Patho- Miiller's ' Physiology,' Eng. translat., 



logy,' translat. bv Dr. Chance, pp. p. 290. 

 123, 126, 294- Claude Bernard, 'Des 



