FUNCTIONS OF PARENCHYMA.—CELL-FORMATION. 7 
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CHAPTER 1, 
SPECIAL PHYSIOLOGY OF THE ELEMENTARY STRUCTURES, 
AND OF THE ORGANS OF NUTRITION. 
Section. 1. PHystotocy oF THE ELEMENTARY STRUCTURES. 
1. Functions or PARENCHYMATOUS CELLS.—As the simplest 
forms of Vegetable life, such as the Red Snow Plant (Proto- 
coccus nivalis) (fig. 1), consist of a single cell of a parenchy- 
matous nature, such a cell is necessarily capable of performing 
all the actions appertaining to plant life. Parenchyma also 
constitutes the whole structure of Thallophytes, as well as the 
soft portions of all plants above them ; hence the physiology of 
parenchymatous cells is of the first importance. The more im- 
portant vital actions of these cells are: (1) Formation of new 
cells ; (2) Absorption and transmission of fluids ; (8) Movements 
in their contents ; and (4) Elaboration of their fluid contents, 
and production of the various organic compounds of the plant. 
(1) Formation of Cells (Cytogenesis).—All plants, as we have 
seen (p. 21), in their earliest conditions, are composed of one or 
more cells, hence all the organs which afterwards make their 
appearance must be produced by the modification of such cells, 
or by the formation of new ones. 
The subject of cell-formation or cytogenesis has for many 
years engaged the attention of able physiologists, and by their 
united labours we have now arrived at tolerably definite con- 
clusions upon the main points of the inquiry, although some 
of the subordinate ones are still involved in obscurity. 
New cells can only be formed from the thickened semi-fluid 
matter called protoplasm ; hence cells can in no case be formed 
without the influence of living organisms. The nature of pro- 
toplasm has been already fully described. By various observers 
this formative matter of cells has also been called organisable 
matter, vegetable mucilage, cytoblastema, &c. The cell-wall or 
membrane of cellulose takes no part in the formation of cells. 
Each cell or elementary part consists of two kinds of matter, 
or of matter in two states: the one termed by some germinal 
matter, which is vitally active ; the other, formed material, which 
is physiologically dead. The protoplasm, primordial utricle, 
and nucleus of vegetable cells are of the first kind, and the cell- 
wall—which Dr. Beale has shown to be not a necessary part of 
the cell—the starch granules, &c., are examples of formed 
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