BOTANY.. 9 



the epidermis and its appendages being merely tlie general investment. 

 The axis consists of a root and a ston., growing generally in diametrically 

 opposite directions. The axis is produced by the development of a spore, 

 an embryo, or a leaf-bud, in two opposite directions. A spore is a young plant 

 produced in the interior of another, Avithout any agency of sexes, and 

 having no determinate point of growtli. An embryo is a young plant 

 produced by the agency of sexes, and situated -svitbin a seed, having a 

 determinate point or points of growth. A leaf-bud is a young plant 

 produced without the agency of sexes, inclosed within rudimentary leaves or 

 scales, and developed on the outside of a stem. The spore and embryo 

 propagate the species in the person of distinct individuals ; the leaf-bud 

 propagates the species in the form of an aggregation of individuals. When 

 the vital action of either spore, embryo, or bud, is excited, development 

 takes place upwards, downwards, and laterally or horizontally ; in the first 

 case causing an elongation of stem, in the second of root, in the third 

 producing an increase in thickness. 



The root, or descending axis, is distinguished fi-om the stem by the 

 absence of normal buds and of stomata ; in exogens there is generally no 

 pith, although a medullary system is present. The objects of the root are 

 twofold : to fix the plant firmly in the earth, and to absorb nutritious 

 substances from the soil. Although roots are generally subterranean, they 

 may sometimes be aerial. Such roots occur in epiphytes, or air plants, as 

 also in species of Ficus, well shown in the Indian Banyan. In this case 

 they are called adventitious, or abnormal. Green-colored aerial roots 

 contain stomata. In certain parasites, as the Dodder or Cuscuta, roots are 

 sometimes produced in the form of suckers, which enter the cellular tissue 

 of the plant preyed upon. Hoots exposed for a long time to the air, 

 sometimes lose their fibrils and develope abnormal buds. 



The /o/7« of roots varies exceedingly with the manner in which the axis 

 descends and branches. When this central axis goes deep into the ground, 

 tapering towards the apex, and without dividing, a tap root is produced. 

 When this tap root becomes somcAvhat shortened, and at the same time 

 succulent, it constitutes the conical root, as in the carrot ; Avhen there is a 

 slight rounding at both extremities, instead of a straight outline, the root is 

 fusiform, as in the radish ; when the axis is nuich shortened in proportion 

 to the thickest diameter, Ave have the napiform, root of the turnip ; if the 

 root end abruptly, as if bitten ofi", it is called prcemorse ; it may also be 

 tiDisted. 



When the descending axis is very short, and at once divides into a 

 number of nearly equal thin fibrils, the root is fibrous, as in many grasses ; 

 Avhen these fibrils arc short and succulent, the root is fasciculated ; when 

 the fasciculi are uniform and arranged like coral, the root is coralline ; 

 when some of the fibrils are developed in the form of starchy tul)ercles, the 

 root is tubercular ; it is nodulose Avhen the fibrils enlarge in cei-tain parts 

 only ; nioniliform Avhen the enlargement is at regular intervals, and of 

 nearly equal size, like a string of beads. The root may also be annulated, 

 Avhen divided by constrictions into partial rings ; placentiform, Avhen 



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