258 THE MICROSCOPE. 



The successive changes in the cell contents furnish 

 other very important characteristics, such as the dis- 

 appearance and re-absorption of the nucleus ; this occurs 

 in every cell at some period of its existence ; in the cells 

 of the higher plants, the inner membrane, or primordial 

 utricle, entirely disappears. The Algae, and some few- 

 unicellular plants, form an excej3tion to the rule. In the 

 animal, the enlargement of the cell-wall takes place in a 

 uniform manner, whereas in the plant this is effected by 

 a deposition of successive layers on its inner surface, in the 

 shape of continuous rings, spiral bands, or other inter- 

 mediate forms. Then the wall not only increases in size, 

 but appears to possess a power of separating and appro- 

 priating certain substances, as lime, silica, lignine, &c, 

 which form the so-called cuticle. In animals as well as 

 in plants, new cells are formed within the old cells ; but 

 in the former, this process of a new formation begins in 

 the extracellular fluid, while in the latter it is mostly 

 endogenous. Multiplication of vegetable cells is effected 

 by three different modes : 1 st, Many nuclei appear in the 

 maternal cell floating together with granular matter ; 

 around each collects a minute vesicle, this gradually 

 increasing fills the maternal cell, which is eventually 

 absorbed. 2d, The internal substance of the cell divides 

 into two or more portions, each being furnished with a 

 nucleus. 3d, In the third mode of multiplication, the 

 wall itself of the maternal cell becomes gradually con- 

 stricted, and divides into two portions.* 



* "In most cells, especially when young, a minute, rounded, colourless 

 body may be seen, either in the middle or on one side, called the nucleus. This is 

 very distinct in a cell of the pulp of an apple : and within this nucleus is often 

 to be seen another smaller body, frequently appearing as a mere dot, called the 

 nucleolus. 



" The nucleus is imbedded in a soft substance, which fills up the entire cell ; 

 this is the protoplasm fprotos, first, plasma, formative substance). As it is very 

 transparent, it is readily overlooked ; but it may usually be shown distinctly 

 by adding a little glycerine to the edge of the cover with a glass rod, when it 

 contracts and separates from the cell-walls. The protoplasm in some cells is 

 semi-solid, and of uniform consistence, while in others it is liquid in the centre, 

 the outer portion being somewhat firmer, and immediately in contact with the 

 cell-wall. In the latter case it forms an inner cell to the cell-wall, and is called 

 the primordial utricle. The terms ' protoplasm ' and ' primordial utricle ' are 

 however used by some authors synonymously. 



"The protoplasm is the essential portion of the cell, and it forms or secretes 

 the cell-wall upon its outer surface in the process of formation of the cell, con- 

 sidered as a whole. It is alao of different chemical composition, from the cell 

 wall being allied in this respect to animal matter. "^Griffitlu. 



