X INTRODUCTION. 



9. But roots under favorable circumstances are developed from other parts of 

 the plant. These are called Secondary Roots. 



10. Aei-ial Roots are those which spring from the stem or branches above 

 ground. In some, as in many Endogenous Plants, they proceed from the lower 

 joints of the stem ; in others, as the Mangroves and Fig-trees of South Florida, 

 they descend from the branches, and at length, penetrating the soil, form new 

 stems in all respects similar to that of the parent tree. The tendril-like roots of 

 some climbing stems are also of this class. 



11. Epiphytes or Air-Plants, of which the Tillandsia and Epidendrum are ex- 

 amples, are those which are borne on the trunks or branches of trees, but draw 

 their nourishment from the air. 



12. Parasites, like Air-Plants, grow on other plants ; but their roots, pene- 

 trating the substance of the supporting plant, feed upon its juices. Some, as 

 the Mistletoe and Dodder, fix themselves upon the trunk or branches ; others, 

 like the Beech-drop, upon the root. 



3. The Stem. 



13. The Stem, or Ascending Axis, is that part of the plant which grows up- 

 ward into the air and light, bearing leaves and flowers. It exists, under various 

 modifications, in all flowering plants ; but in those which are said to be stemless 

 or acaulescent, it is very short, or concealed in the ground. 



14. It consists of a succession of leaf-bearing points, or Nodes, separated by 

 naked joints, or Internodes. The growing points, which are protected by reduced 

 leaves in the form of scales, are called Buds. These are terminal, when they ter- 

 minate the axis ; axillary, when they spring from the axil of the leaves ; that is, 

 from the point where the upper surface of the leaf joins the stem ; and adventi- 

 tious, when they are developed from any other part. 



15. Simple stems grow by the development of the terminal bud alone ; branch- 

 ing stems expand indefinitely from the axillary buds also. The ultimate divis- 

 ions of the branches are called branchlets. 



16. The jointed stem of Grasses and similar plants is a Culm. 



17. The thick and .simple stem of the Palmetto is a Caudex. 



1 8. A Rhizoma, or Rootstock, is a perennial stem, commonly creeping on the 

 ground, or beneath its surface, developing annually a bud at the apex, while 

 the older portion decays. 



19. A Tuber is a subterranean branch, excessively thickened by the deposition 

 of starchy matter, and furnished with minute scales, having concealed buds (eyes) 

 in their axils. 



20. A Corm is a solid globular subteiTanean stem, filled with starchy matter, 

 with a bud at the apex and roots below. 



21 . A Bulb is a short subterranean stem, made up of the thickened bases of 

 leaves, in the form of persistent scales. It is tunicated or coated, when the scales 

 are large and wrapped one within the other ; and scaly, when these are small 

 and imbricated. Small aerial bulbs, such as are borne in the axil of the leaves 

 of the Tiger-Lily, and among the flowers of the Onion, are called Bulblets. 



22. A Stolon is a branch which bends to the earth, strikes root, and forms a 

 new plant. 



