4 PART I.— ORGANOGRAPHY. 



the plant to climb, a leaf or a branch is converted into a ten- 

 dril, and if the good of the species requires that it be defended 

 against predacious animals, hairs are modified into prickles, or 

 branches or leaves into thorns. Thus it happens that the same 

 organ exists under such various forms and disguises, and the skill 

 of the botanist is nowhere better shown than in his ability to 

 penetrate the character of these disguises and determine what 

 organs have been modified to produce them. 



THE ORGANS OF VEGETATION. 



Some of the flowerless plants below mosses possess clearly 

 defined plant-hairs, and in rare instances an indistinct differ- 

 entiation of stem and leaf. In the mosses the distinction becomes 

 sharp and clear, but they do not possess roots. It is not till we 

 reach the Pteridophytes, or highest group of flowerless plants, 

 that we find a complete differentiation of all the vegetative 

 organs. The order of their evolution, therefore, seems to be as 

 follows : First, plant-hairs, or trichomes, then leaf and stem, 

 and lastly roots. In complexity of structure plant-hairs rank 

 lowest and leaves highest, while roots are next to plant-hairs, 

 and stems next to leaves. 



CHAPTER I.— THE ROOT. 



The root may be defined as that part of the plant-axis which 

 does not bear leaves. Roots are ordinarily subterranean in their 

 habits, and serve the double use of attaching the plant securely 

 to the soil and of enabling it to absorb from it the necessary 

 food. These are their normal uses, but they sometimes take 

 upon themselves additional functions. The roots of the Carrot, 

 Beet and Turnip, for example, not only subserve these functions, 

 but also that of storehouses for food. These plants are bien- 

 nials, and during the first year of their growth they store away in 

 their fleshy roots great quantities of nutrient materials, which, 

 during the succeeding year is expended in the production of 

 flowers and fruits. Many perennial herbs, like the Dahlia, though 

 the above-ground parts perish at the close of every season, are 



