70 THE STEMS OF PLANTS. 



cellular organs as the lenticular glands of the willow, and to include such reservoirs aa 

 the vittse or receptacles of the volatile oils of plants. 



Glands are sessile or sitting when resting immediately upon the cutis, aa may be 

 teen near the base of the ovary or seed-vessel of such pod-bearing plants as the Cruci- 

 ferae. They are also found upon the calyx of some campanulas, and upon the petiole 

 or foot-stalk of the leaves of the peach, the cassias, and the passion flower. Their 

 forms, colour, and appearance are very various, and of many it may be doubted if they 

 are true glands. 



Stalked glands (Fig. 118), are such as are elevated from the cuticle by something 

 in the nature of a hair, and are simple if they consist of one or perhaps more cells and 

 have a stalk of but one conduit, and compound where there are several cells and several 

 conduits. This division of glands has been termed indifferently stalked glands or 

 glandular hairs. They are common in the rose and brambles, the Hypericums, the Rue, 

 the Tatropha, the Snapdragon (Antirrhinum!) , the Lysimachis, the Drosera or sun-dew, 

 and many other plants. In the sun-dew the hair of the leaf has an internal fibre, and is 

 therefore a fibre cell ; and the gland head consists of several layers of cells, the outer 

 ones being small and cuticular, whilst the inner ones are long and columnar, and some- 

 times contain a spinal fibre. 



Before proceeding to a consideration of the stems of wooded plants we will direct 

 attention to two modifications which are met with, not exclusively, but chiefly, in 

 herbaceous plants viz., first an enlargement of that part which is under ground, and 

 which lies between the roots or rootlets below, and the true stem above ; and secondly, 

 such stems as take a horizontal rather than a perpendicular course above ground. These 

 are termed respectively subterranean and aerial stems. 



Subterranean stems, as the potato, onion, and turnip, include almost all the recep- 

 tacles of starch, except seeds, provided for the use of man. There can be no doubt as 

 to their analogies, seeing that they do not possess the anatomical and physio- 

 logical properties of roots, and do, notwithstanding their deformity, resemble stems. 

 They are commonly arranged under four heads the bulb, conn, tuber, and creeping 

 fltem. 



The creeping stem (soboles), unlike the others is unimportant as an article of food, but 



yet is of great value from the property which 

 it has of insinuating itself rapidly amongst 

 the sandy particles of loose soils, and binding 

 them together. It may thus lay the foundation 

 of hills of sand which shall suffice to resist the 

 encroachments of the sea. It is represented by 

 the couch grass (Triticum repcns), the bane of 

 farmers, not only from the property above 

 mentioned, but from the rapidity with which it 

 multiplies itself whenever the stem is broken 



Fi*. 118.-The underground stem of the ^ the farmers> efforts to clear the land ' 

 potato (Solanum tuberosum), -with its The tuber or potato is an irregularly ovoid 



S b o^ pS Sct^to^the? enlargement of the stem, having upon its surface 

 by small bundles of fibre, 6. a number of growing points, familiarly termed 



eyes. The tubers of the same plant are all con- 

 nected together and to the parent stem by 

 single bands of small diameter, consisting chiefly of woody fibre for the purposes of the 



