34 SCHLEIDEN'S THEORY. [BOOK i. 



remains loose in the cavity. It is, however, in time absorbed, 

 and it is only after its absorption has occurred that, as Schlei- 

 den believes, the process of depositing secondary layers begins. 

 The Cytoblast appears, however, sometimes to have a perma- 

 nent existence, as in the pollen of Larix europsea, and in those 

 hairs in which a circulation of the sap is observable ; in them 

 Schleiden has remarked (and the observations of myself and 

 others coincide with his), that all the currents proceed from 

 the Cytoblast, and return to it as to a common centre. Mr. 

 Henfrey objects to this theory upon the ground that two cells 

 may be formed by the division of a parent cell, without any 

 change in the position of the contents. This he regards with 

 much reason as a decided proof that the two new cells did 

 not .originate free, of small size, and afterwards grow to fill 

 the parent cell, because in that case the original contents of 

 the parent cell must have been outside the new cells, and there- 

 fore, in order to be found in the interior of the latter, must 

 necessarily have been dissolved, absorbed, and re-deposited, 

 which has not been seen to happen. 



F. Cells proceed from nucleal vesicles (Cytoblasts} , inclosing 

 dense mucilage, with one nucleolus or more. These nucleoli 

 are probably also vesicles of a mixed order, filled with mucilage. 

 The nucleal vesicles^ which may be either free or attached to 

 the wall of a cell, send out many thread-like currents of sap 

 into the cavity of the cell, and thus become foci of vitality, by 

 whose action the walls of the cell are formed and nourished. 

 This theory, which in many respects is like that of Schleiden, 

 has been proposed by Carl Nageli, whose elaborate and admi- 

 rable memoir on cell formation has been well translated for 

 the Ray Society by Mr. Henfrey. The following extract will 

 assist the reader in understanding his peculiar views : 



" Cell-nuclei (Cytoblasts) occur in all classes and orders of 

 plants. The number of plants in which they have not yet 

 been found, is comparatively very small. The exception in 

 these cases may justly be attributed to insufficiency of obser- 

 vation, on account partly of the minute size of the nascent 

 cells (in Lichens, many fungi), partly of the extraordinary 

 size of the cells (Siphonese), and partly of the opacity of the 

 contents of the young cells (some Confervse and Siphoned.) 



