178 VEGETABLE ORGANOGRAPHY. 



from one another, upon a growing stem or branch, we 

 see, when its increase in length stops, that the marks 

 are all separated from one another, but all remain at 

 perceptibly equal distances ; whence Duhamel, to whom 

 this experiment is due, concluded that the elongation 

 took place throughout the whole length at once, during 

 the first year. One would have arrived at the same 

 results from the simple observation of natural facts : all 

 the leaves already exist upon the growing branch, but 

 very near one another. In following their develop- 

 ment we see, it is true, that the elongation of the 

 branch commences at the base ; but when it stops 

 growing, the leaves are much more distant from each 

 other than they were before, but at nearly equal dis- 

 tances ; sometimes those of the higher end are nearer 

 each other, probably on account of the incomplete 

 development of the branch. The observation of the 

 Lenticels, Glands, Hairs, or Stings, whicli may be 

 found regularly disposed upon the branches, leads to 

 the same results. We may, then, regard it as certain, 

 that stems or branches, during the first year, elongate 

 nearly equally throughout their whole length, if we con- 

 sider them together ; but when we examine the increase 

 of this branch in part, we see, with Cassini, that each 

 merithallus, or internode, grows principally by its lower 

 part ; or, in other terms, that its superior part is formed 

 before the lower, the extension of which produces the 

 increase in length : thus it is easy to see in the meri- 

 thalli of Ephedra, or of the Caryophylleae, that the 

 lower part is softer and younger than the upper. The 

 same law is found in grasses : perhaps it is common to 

 all stems, and is essentially owing to the nutritive action 

 of the leaf upon the merithallus which bears it. 



After this first period, a branch or stem grows no 

 more, and the plant only elongates by the addition of a 



