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. (viticida, 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 Cucumber and the Vine. This term is now 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 acaidis really means, is that the stem is very short. 
The Pseudohulb is an enlarged aerial stem, resembling a 
tuber, from which it scarcely differs, 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. 
The internal ^ructure 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 
