66 ORGANOGRAPHY. BOOK I. 



was thus applied, because, when the layer is separated from its 

 parent, its lower end resembles a hammer head, of which the 

 new plant represents the handle. 



The Offset, fig. 29. {propaculum. Link), is a short lateral 

 branch in some herbaceous plants, terminated by a cluster of 

 leaves, and capable of taking root when separated from the 

 mother plant, as in Sempervivum. It differs very little from 

 the runner. 



The Rootstock, fig. 27. (rhizoma), is a prostrate thickened 

 rooting stem, which yearly produces young branches or plants. 

 It is chiefly found in Iridese and epiphytous Orchideae, and is 

 often called caudex repens. The old botanists called it cervix, 

 — a name now forgotten. 



The Vine, fig. 30. {viticula, Fuchs.), is a stem which trails 

 along the ground without rooting, or entangles itself with 

 other plants, to which it adheres by means of its tendrils, as 

 the Cucvunber and the Vine. This term is how rarely em- 

 ployed. De CandoUe refers it to the runner or sarmentum ; 

 but it is essentially distinct from that form of stem. 



If a plant is apparently destitute of an aerial stem, it is 

 technically called stemless {acaulis), a term which must not 

 however be understood to be exact, because it is, from the 

 nature of things, impossible that any plant can exist without 

 a stem in a greater or less degree of developement. All that 

 the term acaulis really means, is that the stem is very short. 



The Pseudohulh is an enlarged aerial stem, resembling a 

 tuber, from which it scarcely difPers, except in its being formed 

 above ground, in having a cuticle that is often extremely hard, 

 and in retaining upon its surface the scars of leaves that it 

 once bore. This is only known in Orchideous plants, in 

 which it is very common : the tuber of Arrow-root is inter- 

 mediate between the Pseudobulb and the genuine tuber. 



3. Of its Internal Modifications. 



Tlie internal structure of the stems of Flowering plants, is 

 subject to two principal and to several subordinate modifica- 

 tions. The former are well illustrated by such plants as the 



