Vlll RUDIMENTS OF BOTANY. 



d. Abrupt, when the fusiform root is as it were cut off suddenly. 



e. Fibrous, a collection or bundle of fibres connected by a common head 

 and often merely by the base of the stem ; as in the Grasses. 



f. Fasciculated, when the fibres swell out slightly in the middle. 



g. Ttibermis or tuber if era us, when some of the branches or fibres assume 

 the form of rounded knobs. These should not be confounded with true 

 tubers, which are properly short subterranean stems, usually containing 

 eyes or buds from which new plants arise. 



h. Palmate, when the knobs of the tuberiferous root are branched. 



12. The direction of the root is usually towards the centre of the earth , 

 but it is sometimes contorted or bent upwards and downwards in a zigzag 

 manner ; or creeping when it proceeds laterally at right angles from this. 

 These have often been confounded with subterranean branches; the last 

 of which only are troublesome to the agriculturalist. 



13. This is the part which springs upwards during the germination of a 

 a seed ; it is the intermediate body between the root and the leaves. 



14. When the stem of a plant arising from a seed is evident, the plant is 

 termed caulescent ; and when not apparent, or scarcely so, the plants have 

 received the name of acanles, or stemless. 



15. When the stem instead of ascending, stretches either wholly or in 

 part, under ground, emitting here and there roots from below and branches 

 or leaves which rise upwards, it is called a rhizoma; or if it do not emit 

 fibres, a cormus or conn. The bulb is a very short stem, consisting of a num- 

 ber of scales, which in growing shoots forth a flowering stem from the cen- 

 tre, and sends out roots from the base. 



16. Stolons or runners are long stems of a peculiar nature issuing hori- 

 zontally from a plant, and emitting only from the extremity roots and leafy 

 buds ; as in the Strawberry. 



17. The stem varies in structure, in three principal modes. 



1 8. In vascular plants it is either formed by successive additions to the 

 outside of the wood, when it is called Exogenous ; or by successive additions 

 to its centre, when it is called Endogenous. In cellular plants it is formed 

 by the union of the base of the leaves, or by a simple elongation or dilata- 

 tion where no leaves or buds exist. 



19. The stem of Exogenous plants may be distinguished into the pith, 

 the medullary sheath, the wood, the bark, the medullary rays, and the 

 cambium. 



'JO. The pith is a mass of spongy cellular tissue occupying the centre of 

 the stem. 



21. The medullary sheath surrounds the pith, and consists of spiral vessels 

 and ducts. It communicates on one side with the pith and on the other 

 with the medullary rays, leaf-buds and veins of the leaves. 



22. The wood lies upon the medullary sheath and consists of concentric 

 layers, one of which is formed every year. These layers are composed of 

 cellular tissue, woody fibre and ducts, and are traversed by the medullary 

 rays composed of cellular tissue, and connecting the centre with the cir- 

 cumference. The fully formed or central layers are called the heart-wood 

 and the exterior the alburnum. 



