34 PKOTOPLASMIC THEORY BEFORE 1860 A. BRAUN. 



activity always stands in inverse proportion to the physiologi- 

 cal activity of the cell. In youth, thin, soft, and extensible, 

 the cell coat allows abundant nutrition and advancing growth ; 

 subsequently thickened and therewith hardened by the deposit 

 of lamellas, it compresses the contents within continually nar- 

 rower boundaries, more and more excludes intercourse with the 

 external world, and puts a term to growth. Thus the life of 

 the plant builds its tomb in the very cell dies away at last in 

 its own work" (p. 155). 



That the origin of the cell precedes its enclosure by a cell 

 membrane is best shown by the cases in which it originates 

 free, that is, without contact with the mother-cell, or where it 

 becomes free by being expelled immediately after its produc- 

 tion, e.g., in the swarm cells, or active gonidia of the Algae. 

 These possess no cell membrane separable from the contents as 

 long as the motion lasts, and must be regarded as bounded 

 merely by the primordial utricle which is intimately connected 

 with the contents (156). Many other proofs of the position 

 are given, that the cell membrane is formed by secretion on the 

 surface as stated by Naegeli, but he is not decided whether the 

 primordial utricle of Mohl exists as a separate envelope, or is a 

 mere lining of protoplasm as stated by Naegeli, and he agrees 

 with the latter in the absence of a nucleus in many unicellular 

 Algse. In the formation of the starch granules of the hydro- 

 dictyon, he considers that the process is by deposition of layers 

 on the surface as was held by Fritsche and Schleiden ; and that 

 the starch is like the cell membrane, secreted by the proto- 

 plasm. " The idea of origin of cells outside, between or on the 

 surface of existing cells, formerly advocated by Mirbel has 

 proved untenable " (227). " It is a mistake to apply the word 

 cell sometimes to the cell with a membrane, sometimes to the 

 cell without a membrane, and sometimes to the membrane 

 without the cell. Since the contents of the cell constitute the 

 essential part of it, since it forms, before the secretion of the 

 (cellulose) membrane, a separate entity possessing its own 

 proper membranous boundary (the primordial utricle), we must 

 call this internal body the cell proper, unless we restrict the 

 term cell to the enclosing wall or chamber, and give the internal 



