20 



NTRODUCTION. 



Prickles are also appendages oFthe cuticle, composed of indurated cellular 

 tissue, and differ from thorns which proceed from the wood. 



Organs of Nutrition. 



The trunk or axis of a plant consists of two parts, growing in opposite 

 directions ; one, ascending or the stem ; one, descending, or the root. The 

 point of junction of these is called the crown, neck, or collar. 



The Root is that part which descends into the earth, acts as a support to 

 the plant, and absorbs nourishment from the soil for its sustenance. It dif- 

 fers from the stem, not only in its mode of growth, but also in being destitute 

 of leaves and other appendages ; in its epidermis being destitute of stomata 

 and in not producing buds, except under peculiar circumstances. Roots, 

 however, are not always produced under ground ; they sometimes arise from 

 any portion of the stem. Thus the branches of most woody plants, when 

 bent down and covered with earth, will put forth roots. This takes place na- 

 turally in many trees in 

 Fi =- 10 - tropical climates, which 



give off roots from their 

 trunk or branches, high 

 above the earth. This 

 phenomenon is very 

 striking in the Ficus re- 

 ligiosa or Banian tree, 

 and in the Pandanus or 

 Screw pine. Roots also 

 attach themselves to the 

 surface of other vegeta- 

 bles, and thence draw 

 their nourishment; plants 

 of this character are called 

 parasitic. Roots increase 

 in length chiefly by the 

 addition of new matter to 

 their extremities. It is 

 by these extremities, 

 called spo?igioles, that 

 absorption takes place. 

 They are of various 

 forms, the principal of 

 which are, 1, Conical or 

 tap root, which is un- 

 branched, and tapers regularly from the crown to the apex, as in the carrot. 

 2. Fusiform or spindle-shaped resembles the first, except that it tapers up- 

 wards as well as downwards. 3. Napiform or turnip-shaped is much 

 broader than long. The small branches of roots are called fibrils or rootlets. 

 If the root divides immediately into fibrils, it is said to be fibrous. When 

 these are thickened and dilated, it is fasciculated, as in the dahlia. Where it 

 is furnished with knobs it is called tuberous, but it should be noticed that in 

 some cases, what are called tuberous roots are in fact altered stems, as in the 

 potato. Bulbs also, which are usually termed roots, are merely subterranean 

 buds ; so also, many creeping roots are really underground stems. The 

 Stem is that portion of the plant which grows in an opposite direction to the 

 root, and gives support to the leaves and organs of reproduction. All flowering 



Pandanus with Aerial Roots. 



