CHLOROPHYLL. 21 



to their form, as vesicles, either rounded or altered in 

 shape by mutual pressure. We have now to notice 

 the matters contained within the cells, or the cell- 

 contents. 



Cell-contents. 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 (PI. I. fig. 2 b). And within this nucleus is 

 often to be seen another smaller body, frequently 

 appearing as a mere dot, called the nucle'olus. 



The nucleus is imbedded in a soft substance, which 

 fills up the entire cell (PI. I. fig. 2 c) ; this is the 

 pro'toplasm (TT/JCOTO?, first, TrXaer^a, formative sub- 

 stance) . As it is very transparent, it is readily over- 

 looked ; 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, as in the lower cell of fig. 2. The proto- 

 plasm in some cells is semisolid and of uniform con- 

 sistence, while in others it is liquid in the centre, the 

 outer portion being somewhat firmer and immedi- 

 ately 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 "proto- 

 plasm " and ' ' primordial utricle " are, however, used 

 by some authors synonymously. 



The protoplasm is the essential part 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 also of different chemical 

 composition from the cell- wall, being allied in this 

 respect to animal matter. 



Chlorophyll (^Xwpo?, green ; (biiXXov, leaf) . On 

 examining a section of any green part of a plant, as 

 the green substance of a Geranium- (Pelargonium-) 

 leaf, it will be seen that the green colour does not 

 arise from the whole substance being coloured, as 



