44 PLANT LIFE ON THE FARM. 



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 neighbour, 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 growing protoplasm within, 

 and by the influx of fluid into the cell by osmosis, pro- 

 ducing a condition of turgescence. The growth of the pro- 

 toplasm 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 subdivision 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 con- 

 cerned 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 con- 



