1.16 VEGETABLE ORGANOGRAPHY. 



It often happens that Prostrate Stems have a tendency, 

 either when they are of a slightly fleshy nature, or 

 when they have distinct nodes or articulations, or when 

 they grow in a moist soil, — it happens, 1 say, that several 

 prostrate stems have a tendency to produce roots; they 

 are called Creeping ( rampantes ) Stems. These roots 

 spring most frequently from near the axils of the leaves, 

 sometimes all along the lower surface of the stem ; they 

 descend, as is peculiar to roots, vertically into the earth, 

 and are not coloured green. 



Upright stems have also a tendency sometimes to pro- 

 trude roots into the air. We see this in a great number 

 of fleshy plants, such as the different species of Cactvs 

 and the Crassulacese, or in certain foreign species of 

 Ficus (PI. 6 shows the development of roots from the 

 lenticels of Ficus elasfica), or especially in Rhizophora. 

 These roots arise in the same manner as in creeping stems, 

 and take a direction straight towards the ground ; they 

 are in general cylindrical and but little branched; in 

 Rhizophora, where they descend from a considerable 

 height, they form kinds of natural arcades of a very 

 extraordinary appearance ; stems endowed with this 

 property are called Rooting (radicantes) by botanists. 



We can, by peculiar modes of culture, excite this 

 production of roots, even in stems which have scarcely 

 any disposition to do so ; and in this consists the art of 

 making layers, for this is the name which is given to a 

 part of a stem or branch, which after having produced 

 roots, is artificially separated from the mother plant. 



Layers are a physiological phenomenon, the study of 

 which cannot occupy us here, since I have thought it 

 necessary to make a remark upon its analogy with the 

 natural state of rooting stems. In all these cases, 

 whether natural or artificial, the roots, which are pro- 

 duced from the branches of trees, spring from the 



I 



