CHAP, ii.] OF GROWTH IN THE VEGETAL KINGDOM. 283 



The development of the plant in length is accomplished in two 



ways ; on the one hand by terminal elongation, due to the evolu 

 ; tion of the bud, which produces internodes or merithalli of new 

 'formation ; on the other, an elongation is effected of the merithalli, 

 'already formed, by the lengthening of their vascular or cellular 



organs. 



The roots scarcely lengthen except from the point, since two 

 I ligatures placed across their course near their extremity never 



separate from each other (Duhamel). 



Most vegetals grow during the whole of their life, either 

 'specially in length, as the monocotyledons, or in both dimensions, 

 ! as the dicotyledons. Growth only slackens more and more in 



proportion as the vegetal tissues become mineralised, and its 

 (complete cessation generally coincides with the death of the 



vegetal. Death, besides, may be partial. In effect, there is no 

 j centralisation in the plant. Every vegetal may be compared to 

 | a polypier. Each bud has its individuality, its own existence ; it 

 'attracts and elaborates the nutritive fluids ; also when a terminal 

 Ibucl dies the branch which bears it dies also. 



The fall of the decayed leaves is determined much less by the 

 autumnal cold than by the termination of the foliaceous growth, 

 due, doubtless, to an excessive degree of mineralization. Many 

 j decayed leaves fall before the appearance of the cold. As to 



the leaves termed persistent, they scarcely differ in this respect 



from the so-called caducous leaves. Instead of falling in a 

 1 mass, they fall one by one, when their growth has reached its 

 [bound. 



Jn the ligneous stems of the dicotyledons, to speak correctly, 

 | death incessantly accompanies life. Every year a certain number 

 I of anatomical elements lose the faculty of growth, of multiplica- 

 ! tion, and at last of receiving nutriment. They become first what 

 ' are called definitive tissues, then little by little are destroyed ; 



but, on the surface of the aubier, where the flow of cambium, 

 of elaborated sap, passes, a new living stratum is formed. In 

 1 proportion as death invades the centre of the stem, vitality takes 



