INTRODUCTORY LESSONS. XV 



trees and most other plants are exogens. Palm-trees, Century-plants^ 

 grasses, and the "small grains," are endogens. 



Serbs are plants whose stems die, at least to the ground, after 

 they have blossomed and matured fruit. These are Annuals when their 

 lives are limited to one season; Biennials when they die the second year 

 — not producing fruit the first year; Perennials when they live on year 

 after year, their stems dying annually down to the ground. The under- 

 ground portions of such stems are called — 



Rootstochs. This name applies more particularly to such stems as 

 grow nearly horizontally under ground, or become thick and fleshy with 

 nutritious matter, which enables the plant to make rapid first growths 

 each year. A rootstock can usually be distinguished from a true root 

 by its bearing buds. 



Bulbs are formed by a peculiar bud growth in which the leaves or 

 tbeir bases become very thick and fleshy, with a store of nourishment, 

 while the stem grows in diameter, but scarcely at all in length. 



Coated or Tunicated Bulbs are those in which the leaves form a 

 succession of envelopes, as in the onion. If the leaves or leaf-bases are 

 narrow, as in the lily, the bulb is Scaly. 



Corms resemble bulbs, but are solid, and have more the nature of 

 Tubers, which are the thickened ends of slender, branching, under- 

 ground stems, as potatoes, ground artichokes, etc. 



Leaves. Collect the leafy stems of many kinds of plants. Ob- 

 serve the arrangement of the leaves on the stems. A few like Erodium 

 (Filaria), the Catcbfly, Pink, Fuchsia, Mint, etc., have Opposite leaves. 

 Possibly you may find a CoUinsia, or stem of Cleavers, with the leaves in 

 Wliorls of three or more. Most plants have Alternate leaves. Tou will 

 find some plants like Plantain, with a bunch of leaves growing from the 

 ground, but no leafy stems. Such leaves come from rootstocks, and are 

 said to be Badical. Plantain, Dodecatheon, Primrose, etc. have the leaves 

 all radical. Many perennial herbs have radical leaves, as well as ordi- 

 nary tstem leaves, and these usually differ more or less from the stem 

 leaves. 



Observe that stems and branches end in buds or flowers, and that 



