VON MOHL NAEGELI. 31 



cates its physical state as follows : " Yet if we reflect that the 

 protoplasm is a viscid fluid which, as its delicate currents show 

 most distinctly, does not mix with the watery cell sap this ap- 

 pearance becomes comprehensible enough; the protoplasm 

 bears the same relation to the cell-sap as a frothing fluid does 

 to the air contained in its bubbles. The unceasing flow and 

 continued transformation of the mass of the protoplasm fur- 

 nish most distinct proof that we have to do with a fluid and 

 not with an organized structure." 



The next important contribution to the subject was made by 

 Naegeli* in 1844 and 1846. Although he admits the possi- 

 bility of spontaneous generation of the first cells of plants and 

 animals apparently for the sake of theoretical completeness, 

 yet he lays down the law that all ordinary cell formation takes 

 place exclusively from pre-existing cells. This applies both 

 to the vegetable and to the reproductive] cell formation (134). 

 He denies Schleiden's theory that mucilage-granules unite to 

 form nucleoli, and these to form nuclei, and says that the em- 

 bryo-sac when cell formation is commencing contains no gran- 

 ules (105). In all cases of cell multiplication it is the contents 

 which divide, grow, and cover themselves with membrane ; in 

 vegetative cell formation only two cells are formed by the di- 

 vision of the parent cell ; in the reproductive there may be 

 from one to an indefinite number (137). The individualization 

 of the contents for the purpose of cell formation takes place 

 under four forms which he describes. But they all include 

 two stages : " first the isolation or individualization of a por- 

 tion of the contents of the parent cell ; the second consistsin 

 the origin of a membrane around individualized portions of 

 the contents " (123). In all these cases it is the mucilaginous 

 cell contents corresponding to the protoplasm of Mohl which is 

 the active agent, and " whether the mucilage be free or lie in 

 contact with a membrane it makes no difference in its func- 

 tion " (125). " The cell membrane is an investment lying upon 

 the surface of the contents, secreted by the contents them- 

 selves " (128). It is never a deposit from the fluid as Schleiden 



* "On the Nuclei, Formation, and Growth of Vegetable Cells." 

 Bay Society, 1849, p. 95. 



