48 PLANT LIFE ON THE FARM. 



these growing points at definite spots, where new cells are 

 always forming during the active period, new growth may 

 occur in isolated spots by the formation of growing cells in 

 the midst of or between others that have lost their faculty 

 of growth, and thus growth in the substance of the plant 

 may take place by intercalation as well as at the extre- 

 mities. 



To repeat, then, true growth consists in the formation of 

 new protoplasm from the old, and in the division of the 

 protoplasm into new cells. This division takes place 

 especially and primarily, so far as growth in length is 

 concerned, at certain definite places called growing points. 

 The new tissues thus formed are at first wholly cellular, 

 some of the constituent cells retaining the faculty of sub- 

 division, though sometimes not manifesting it till a later 

 period ; while others become modified in various ways as 

 growth goes on, forming wood-cells, fibres, epidermis, and 

 so on. 



Perm as dependent on Growth. If we could suppose 

 the degree or intensity of growth to be equal on all sides, 

 and without impediment or obstacle, the result would be a 

 spherical plant ; and such plants do exist, but, in the great 

 majority of cases, the conditions are such that growth is 

 greater in amount in one direction than in another; or it 

 maybe that while part remains stationary another part grows, 

 the result being a change of form. In the case of the main 

 root and stem, the principal direction of growth is vertically 

 upwards and downwards ; in the case of leaves, the main 

 direction of growth is horizontal, so that while a stem or a 

 root may be divided from above downwards into two nearly 

 equal halves, one half the reflex of the other, a leaf must be 



