46: PLANT LIFE ON THE FARM. 
the molecules of cell-membrane are separated by the pres- 
sure caused by the turgid protoplasm, and into the inter- 
stices so formed, new molecules of membrane formed by 
the protoplasm are, as it were, squeezed. ‘The process is 
as if a number of grains of sand were laid upon a table, 
each grain just touching its neighbor, and then a new 
grain were forced in between two others, only in this case 
the new grain is formed in the cell itself. The requisite 
pressure is afforded, in the case of the cell, by the grow- 
ing protoplasm within, and by the influx of fluid into 
the cell by osmosis, producing a condition of turgescence. 
The growth of the protoplasm itself takes place precisely 
in the same way as that of the cell membrane—viz., by 
the formation of new particles, which are squeezed in by 
intercalary growth between the older ones. New matter 
is also deposited on the outer surface of the protoplasm 
or inner surface of the cell wall. 
Lastly, growth is effected, not merely by extension of 
old cells, or by incorporation of new materials with old, 
but by actual increase in the number of cells. This 
increase in number has been brought about by the sub- 
division of the protoplasm into two or more segments, 
each of which becomes invested by cell-membrane. 
For full details as to the various ways in which division 
of the protoplasm and the formation of new cells take 
place, reference must be made to text books. What has 
been here said is sufficient to indicate the general nature 
of growth in the organs—with which we are here most 
concerned—the root, the stem, and the leaf. 
Growing Points.—As has been stated, all the parts of 
plants are at first wholly cellular and structurally indis- 
tinguishable ; but, as growth goes on, not only their 
outer form alters, but the form and arrangement of their 
constituent cells also, so that various tissues—fibrous, 
woody, vascular, or epidermal—are formed ; and thus it 
