14 Principles of Plant Culture. 
The higher plants and animals are made up of many cells 
united, and in these, the cells assume different forms and 
properties in the different organs (Fig. 3). In some cases, 
Fic. 2. Part of a filament of a species of Spirogyra, a plant consisting of a 
single row of cells united at their ends. The places where the cells join are indi- 
cated by tbe vertical lines. Highly magnified. 
the united cells may be readily separated from one another, 
which shows each cell to be more or less an independent 
structure. As a rule, each cell is surrounded by its own 
closed cell-wall. 
13. Protoplasm  (pro’- 
to-plasm). Living cells con- 
sist of a transparent, jelly- 
like substance called protop- 
lasm, which manifests the 
various phenomena of life. 
Protoplasm may exist either 
in an active or dormant 
state. In the active state 
it requires both nourishment 
and oxygen; in the dormant 
state it may exist for a con- 
siderable time without either, 
and is far less susceptible to 
Fic 8. Showing cells of the apple leaf 
: in a section from its upper to its lower 
external influences than in surface. Highly magnified. The spaces 
marked I are cavities between the cells. 
jts active state. The protop- 
lasm contained in plants during their rest period (172), in 
mature air-dry* seeds, and in the lower animals during their 
torpid condition is in the so-called dormant state. 
* Material is said to be ‘air-dry ” when it is as dry as it will become by expo- 
sure to the air at ordinary temperatures. 
