OUTLINES OF BOTANY. XXXV 



cult to distinguish until the seed begins to germinate. Their observation, how- 

 ever, is of the greatest importance, for it is chiefly upon the distinction between 

 the embryo with one or with two cotyledons that are founded the two great 

 classes of phaenogamous plants, Monocotyledons and Dicotyledons. 



167. Although the embryo lies loose (unattached) within the seed, it is 

 generally in some determinate position with respect to the seed or to the whole 

 fruit. This position is described by stating the direction of the radicle next to 

 or more or less remote from the hilum, or it is said to be superior if pointing 

 towards the summit of the fruit, inferior if pointing towards the base of the 

 fruit. 



§ 15. Accessory Organs. 



3 68. Under this name are included, in many elementary works, various ex- 

 ternal parts of plants which do not appear to act any essential part either in 

 the vegetation or reproduction of the plant. They may be classed under four 

 heads : Tendrils and Hooks, Thorns, and Prickles, Hairs, and Glands. 



169. Tendrils (cirrhi) are usually abortive petioles, or abortive peduncles, 

 or sometimes abortive ends of branches. They are simple or more or less 

 branched, flexible, and coil more or less firmly round any objects within their 

 reach, in order to support the plant to which they belong. Hooks are similar 

 holdfasts, but of a firmer consistence, not branched, and less coiled. 



170. Thorns and Prickles have been fancifully called the weapons of 

 plants. A Thorn or Spine is the strongly pointed extremity of a branch, or 

 abortive petiole, or abortive peduncle. A Prickle is a sharply pointed ex- 

 crescence from the epidermis, and is usually produced on a branch, on the 

 petiole or veins of a leaf, or on a peduncle, or even on the calyx or corolla. 

 When the teeth of a leaf or the stipules are pungent, they are also called prickles, 

 not thorns. A plant is spinous if it has thorns, aculeate if it has prickles. 



171. Hairs, in the general sense, or the indumentum (or clothing) of a plant, 

 include all those productions of the epidermis which have, by a more or less 

 appropriate comparison, been termed bristles, hairs, doivn, cotton, or wool. 



172. Hairs are often branched. They are said to be attached by the centre, 

 if parted from the base, and the forks spread along the surface in opposite di- 

 rections ; plumose, if the branches are arranged along a common axis, as in 

 a feather j stellate, if several branches radiate horizontally. These stellate 

 hairs have sometimes their rays connected together at the base, forming little 

 flat circular disks attached by the centre, and are then called scales, and the 

 surface is said to be scaly or lepidote. 



173. The Epidermis, or outer skin, of an organ, as to its surface and indu- 

 mentum, is 



smooth, when without any protuberance whatever. 



glabrous, when without hairs of any kind. 



striate, when marked with parallel longitudinal lines, either slightly raised 

 or merely discoloured. 



furrowed (sulcate) or ribbed (costate) when the parallel lines are more 

 distinctly raised. 



rugose, when wrinkled or marked with irregular raised or depressed lines. 



umbilicate, when marked with a small round depression. 



umbonate, when bearing a small boss like that of a shield. 



viscous, viscid, or glutinous, when covered with a sticky or clammy exu^ 

 dation. 



scabrous, when rough to the touch. 



tuberculate or warted, when covered with small, obtuse, wart-like protu- 

 berances. 



muricate, when the protuberances are more raised and pointed but yet 

 short and hard. 



c 2 



