134 VEGETABLE CELLS. 



The homogeneous substance lying on the surface of the 

 cell-contents and secreting the membrane, is mucilage 

 (schleim) (albumen mixed with gum and sugar). Either 

 the whole portion of contents individualized through the 

 influence of the nucleus consists of mucilage, or of muci- 

 lage with which other matters are mingled ; in the latter 

 case, however, the extreme outer surface is always formed 

 by mucilage. There are two especial properties of the 

 mucilage which are of essential assistance in the formation 

 of cells. The first is this, that whenever it becomes free 

 or isolated, it acquires a perfectly smooth surface, on 

 which the strongest magnifying power fails to discover the 

 slightest prominences or depressions. A second property 

 is, that where mucilage and other solid matters unite into 

 a definite form, a portion of the mucilage always forms a 

 superficial layer, the other substances being as it were re- 

 pressed by it. The latter may be seen, both when the 

 contents of a ceh 1 (especially of the cells of Algae) flow out 

 in water, and when through injury to the cell the contents 

 become retracted from the walls, and divided into isolated 

 portions. Through the homogeneous mucilage forming a 

 continuous enveloping layer, or any portion of contents 

 becoming individualized, this becomes at once a con- 

 nected whole with definite boundaries. Through the 

 mucilage possessing a perfectly smooth external surface, 

 is produced a membrane, continuous and smooth, even 

 at the very first moment of its formation. 



Having become acquainted with the definition of cell- 

 formation, and in it the conditions necessary to the pro- 

 cess, we will now examine more closely some of its 

 external relations. The cell may originate in another cell 

 or outside cells. In the vegetable kingdom the law holds 

 that all normal vegetative cell-formation takes place solely 

 inside cells ; moreover, that all normal reproductive cell- 

 formation, for the purpose of propagation, likewise occurs 

 exclusively in the interior of cells. Only the first cells 

 of individuals originating through (jeneratio aquivoca, are 

 formed outside cells. 



