104 ON THE PLANT-CELL. 



tinguishes three modes in which vegetable cells originate, which he terms 

 "intra-utriculaire" (the process above descrived), " supra-utriculaire," 

 and " inter-utriculaire." The first only of these modes is proved to exist 

 by actual observation ; the two latter have not been observed, and are gra- 

 tuitous assumptions. 



46. According to Hugo Mohl*, another mode of increase ob- 

 tains in the cells of the Cryptogamia (Conferva), consisting in a 

 circular constriction of the cell, which gradually advancing inwards 

 divides the cell in the middle into two, so that a complete division 

 of the cell into two new ones is effected. 



These researches of Mohl contain the first and (except those of Niigeli 

 and myself) the only actual observations on the multiplication of vege- 

 table cells, f I have never been so fortunate as to observe a complete 

 series of cells in this course of development, although I have frequently 

 examined Potysperma glomerata, the plant which formed the principal 

 subject of Mohl's researches. This has been the case also with Nasgeli, 

 who has explained the error in Mohl's supposition. J 



After Mohl, Meyen has been the principal advocate of this view, be- 

 lieving that he has in numerous instances recognised this process of 

 spontaneous scission, and regarding it as almost a general law in plants. 

 In most of the cases adduced by him, the fact has simply been invented, 

 not observed. In the instance in which he refers to direct observation 

 on the origin of four pollen -cells in the matrix, the fact is exactly the 

 reverse ; with reference to which, compare what is said on the subject 

 of pollen in a subsequent part of this work. 



linger, also, has again propounded the multiplication of cells by scission 

 as a general law in plants ||, but with as little truth as Meyen. Neither 

 has he adduced a single instance in which he had actually observed the 

 process of division. The fact that, in a particular instance, at first but 

 one and afterwards in the same place two cells exist, that near one large 

 cell two others occur which together perhaps have the same circum- 

 ference as the first, does not throw the least light upon the process of 

 multiplication : he has, however, no other facts to rest upon, or at least 

 has not communicated them. 



Whether cell-division occurs generally in plants is still to be deter- 

 mined. Certainly, the condition mentioned in the preceding section is 

 the more frequent one. 



VIII. Of the Termination of Cell-Life. 



47. As soon as the play of chemical affinities has become im- 

 possible in a cell, the latter must be regarded as individually dead. 

 So far, all cells must be considered to have died as individuals which 



* Ueber Vermehrung der Pflanzenzelle durch Theilung. Tub., 1835. 



f To these names must be added that of Mr. A. Henfrey, whose original and in- 

 teresting observations respecting the multiplication of vegetable-cells were first made 

 known at the meeting of the British Association at Cambridge, in 1845, and have 

 subsequently been incorporated in his work entitled " Outlines of Structural and 

 Physiological Botany," Lond. 1847. Mr. Henfrey adopts Mohl's views with some 

 modifications. TRANS. 



\ L. c. Physiologic, vol. iii. p. 123, et seq. 



|[ Bau und Wachsthura des Dicotyledonenstammes, Petersburg, 1840, p. 86, et seq. 



