DEFINITION AND CLASSIFICATION OF STEMS. 65 J 



A scale-leaf stem which remains short, which is clothed with membraneous scales 

 and does not exceed in thickness the foliage or floral stem which often proceeds from 

 it, is called a sucker (surculus). The sucker, beset with scale-leaves, appears as a bud 

 (gemma) so long as the foliage or floral stem has not grown out from it; later it 

 forms to some extent the basis of the foliage or floral stem, and is not very remark- 

 able, especially after its hollowed scale-leaves, as is almost always the case, become 

 detached and fall off. The scaly stem is but seldom developed at the base of the 

 first shoot (plumule) arising between the cotyledons (e.g. in the Moschatel, Adoxa 

 Moschatellina). On the other hand, it is scarcely ever absent from the base of the 

 lateral shoots of woody plants, those bearing leaves as well as those which are 

 terminated by flowers. In the subterranean buds of undershrubs the stem is occa- 

 sionally very thick, and such buds have almost the appearance of bulbs. The 

 subterranean buds, especially those of shrubs and trees, always possess, on the other 

 hand, a short cylindrical or conical stem. 



The tuber (tuber) seems to be to some extent a link between the reduced and 

 the long axes formed by scale-leaf stems. It is always thicker than the shoots 

 arising from it; its scale-leaves are situated so far apart that a clear space is visible 

 between them, and they never cover and envelop one another. The scale-leaves of 

 the tuber are insignificant; they only appear as narrow horizontal bands, or they 

 are merely indicated by ridges and protuberances. In old tubers the scale-leaves 

 are often scarcely recognizable externally. Most tubers are, moreover, very perish- 

 able structures; all those which appear as local thickenings of an underground 

 shoot, of which the Potato (Solanum tuberosum) may serve as a type, grow very 

 quickly, and have a resting-period of about half a year, but perish completely after 

 they have developed shoots from their buds (the so-called " eyes ") which unfold 

 their green foliage above ground in the sunlight. Perennial tubers, whose lower 

 half only is often embedded in the earth, or which are only covered with a thin 

 layer of soil, are much less common. From these spring up every year a few shoots 

 which, however, do not completely exhaust the tuber, but, on the contrary, supply 

 it with materials manufactured by the green foliage in the sunlight, by which 

 means the tissue of the tuber is actually enlarged. These perennial tubers fre- 

 quently look like tuberous leafy stems, and the whole history of development 

 must be known in order to be able to determine and prove that they really are scaly 

 stems. Tubers are generally subterranean. More rarely they are formed above 

 the soil in the axils of foliage-leaves, as, for example, in the Lesser Celandine 

 (Ranunculus Ficaria), where those remarkable little tubers arise, which become 

 detached after the withering of the plant; they afterwards lie on the ground, and 

 have often, where they have been produced in great quantities, given ris 

 myth of " potato rain ". 



Whilst some of the stems which bear scale-leaves are green, others 

 of chlorophyll, and of these latter the following types may be distinguished :- 

 the aerial, thread-like, twining and parasitic stems of the genus Cuscuto', second, 

 the thin subterranean shoots of the Couch-grass (Triticum repens) and of numerous 



