12° VEGETABLE PHYSIOLOGY 
the latter undergoing much subsequent differentiation 
according to their ultimate dimensions and the nature of 
their habitat or environment. 
The protoplasm being the living substance of the plant 
is possessed of certain properties which are not shared by 
Fie 18.—F1iuamMents oF Nostoc. Fie. 14.—Pediastrum, consist- 
(After Luerssen.) ING OF A PLaTE oF CELLS. 
the framework on which it rests. It is, indeed, the centre 
of all the activities which the plant manifests. It assimi- 
lates the food which the plant requires and carries out all 
the chemical processes necessary for life. It constructs 
B 
Fic. 15—VEGETABLE CELLS. 
A, very young; B, a little older, showing commencing formation of vacuole. 
Pp, protoplasm ; 7, nucleus; v, a vacuole. 
the framework of the plant by which it is itself supported. 
It receives impressions from without, and regulates the 
responses which the plant as a whole makes to those 
impressions, both by internal and external movements or 
changes of position. It is only by its powers of responding 
to such impressions that the whole organism is able to place 
