CELLS.— CHLOROPHYLLS. 
35 
plants, such as the various species of Char a , Nitella , 
and Vallisneria , or the hairs of the Groundsel and 
Tradescantia. 
The stem of the Nitella consists of cylindrical cells, 
in most of which a movement of granules may be ob- 
served ; they pass up on one side of the cell and down on 
the other, but never escape into 
adjoining cells. The circula- 
tion may, however, be more 
plainly seen in the Vallisne- 
ria ; a thin layer of one of 
the flattened leaves of this 
plant will exhibit a series of 
oblong cells, as shown in 
Fig. 24, in each of which an 
active circulatory movement 
may be noticed ; among the 
granules so moving may be discerned one larger and 
more transparent than the rest' — the nucleus or cyto- 
blast of the cell, having a nucleolus within it. 
I shall now proceed to describe very briefly some of 
the other contents of cells, such as milky-juices, oils, 
resins, &c , all of which are important to mankind, some 
being universally employed as food, others extensively 
used in the arts. 
Milky-juices are true secretions found in many plants, 
and contained in distinct vessels called milk or laticife- 
rous ducts, formed by the union of elongated cells, which, 
D 2 
FIG. 24 . 
Portion of leaf of Vallisneria 
spiralis. 
of the green granules 
