Ch. IV, 7] GROWTH OF PLANTS 153 



ment of food is in the bark. Accordingly, if the bark be 

 constricted, the passage of food downward from the leaves 

 is stopped, and its accumulation produces a swelling above 

 the constricting object. This happens in botanical gardens 

 where labels are attached by wire, or in shade trees which are 

 strengthened by iron bands placed around them (Figs. 107, 

 155). The swelling may, however, go so far as to make the 

 bark over-arch the constriction and establish a new connec- 

 tion beyond it, thus burying band or wire completely. 



7. The Growth of Stems and Other Plant Parts 



It happens that stems exhibit the principal phenomena 

 of plant growth more clearly than any other parts. Ac- 

 cordingly we may best consider that important subject 

 at this place. 



The growth of the higher plants differs from that of the 

 higher animals in this, that while animals develop a single 

 set of organs which serve throughout life, plants exhibit a 

 constant and indefinite repetition of a few primary organs, 

 — leaves, stems, roots, flowers, fruits, and seeds. But the 

 general mode of growth of an individual leaf, stem, root, 

 or other part is much the same as that of an animal organ. 



The growth of each individual organ or part, whether of 

 animal or plant, exhibits three stages, which often overlap, 

 but commonly are more or less separate. They are, first, 

 development, or formation in the embryonic state : second, 

 enlargement, or increase in size, and third, maturation, 

 or ripening to full functional efficiency. The difference 

 between the stages comes out very clearly in case of the 

 spring vegetation. First, as everybody knows, the flowers 

 and leaves which unfold in early spring were all formed or 

 developed the preceding season, and existed over winter 

 folded compactly away in buds, in which they can easily 

 be found. The microscope shows that most of the cells of 

 those parts are perfectly formed, though small and filled 

 with food. Second, in the early spring the buds, absorbing 



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