36 



THE GARDENER'S ASSISTANT. 



ground stems go by the general name of root- 

 stock or rhizome (fig. 35), and as special varieties 

 of it may be mentioned the tuber, a more or less 



Fig. 85.— Rhizome "f Iris. 



globular or oblong swelling of a branch, as in 

 the Potato; the corm (fig. 3G), a globular dilata- 

 tion of the stem, with a few leaves in the 

 shape of scales outside, as in the Crocus or the 

 Gladiolus; or the bulb, 

 where the scales are nu- 

 merous and the stem rela- 

 tively small (figs. 37, 38). 

 Similar bulbs and tubers 

 may occasionally be found 

 on the stem in the axils 

 of the leaves (fig. 39). 



Creeping roots, so-called 

 (fig. 4 0), are usually slen- 

 der branches, creeping 

 along on the surface of the 

 ground, or just beneath it, 

 provided with leaf-scales, 

 or even true leaves, and 

 giving off roots from their 

 lower surface. A straw- 

 berry runner is a branch 

 of this character, designed, as it would seem, to 

 secure to the young plant at its extremity a 

 new habitation where the soil has not been so 



Fig. 36.— Uoichicum— Corm. 



much exhausted of its constituents as must be 

 the case in the vicinity of the parent plant. 

 Stem Structure. — The general structure of an 



Fig. 37. -Lily-Scaly Bulb. 



Fig. 3S.-Omon-Tunicated Bulb. 



herbaceous stem or shoot has been already 

 referred to, but during its conversion into a 

 woody branch or stem numerous changes occur. 

 The outer skin or "epiderm", at first continuous 

 with that of the leaf, gener- 

 ally disappears, the cellular 

 cortex beneath becomes dif- 

 ferentiated into various por- 

 tions as before stated. Then 

 comes the cambium or forma- 

 tive layer, and within that 

 the wood, encircling a cylin- 

 der of cellular tissue called 

 the medulla or pith. The 

 "wood", or the woody 

 bundles, form a ring of wedge-shaped masses 

 around the pith, the wedge-shaped masses being 

 separated one from the other by rays of cellular 

 tissue passing radially outward from the pith to 



39 — Bulb-beariug Lily 

 —Portion of Stem. 



Fig. 4u— Carex— Rhizome. 



the cambium (fig. 41). These are the medullary 

 rays. The pith and the medullary rays are part 

 of the "fundamental tissue" of which the whole 

 stem or branch in its young state consists. 



