EPIDERMAL APPENDAGES. HAIRS. 29 



occurs, consisting of elongated cells, to which the name of ramenta- 

 ceous hairs, or, ramenta (ramentum, a 

 shaving), has been given. In Palms 

 also a similar substance occurs, called 

 reticulum (reticulum, a net), or mattulla, 

 (matta, a mat). Prickles or aculei, as in 

 the Rose, (fig. 191 a), are hardened hairs 

 connected with the epidermis, and differ 

 from spines or thorns, which have a 

 deeper origin. Setae are bristles or 

 stiff hairs, and the surfaces on which 

 they occur are said to be setose or seta- 

 ceous. Some hairs, as those of Drosera, 

 or sundew, have one or more spiral fibres in their interior. 



58. Various names have been given to the different forms of hairs: 

 they are clavate or club-shaped (clava, a club), gradually expanding from 

 the base to their apex; capitate, having a distinct rounded head; rough 

 or scabrous, with slight projections on their surface; hooked or uncinate 

 (uncus, a hook), with a hook at their apex pointing downwards and to 

 one side; barbed or glochidiate (yX^/V, a barb), with two or more 

 hooks around the apex; shield-like or 'peltate (pelta, a buckler), when 

 attached by their middle, and projecting horizontally on either side (fig. 

 84), as in many cruciferous plants; 



ciliated (cilium, an eye-lash), when 



surrounding the margin of leaves. 



On the pod of the Cowitch (Mucuna 



pruriens), hairs are produced with 



projections on their surface, which cause great irritation when applied 



to the skin. In Venus' Fly-trap (Dioncea muscipula), stiff hairs exist on 



the blades of the leaf (fig. 186 e), which, when touched, cause their closure. 



59. Hairs occur on various parts of plants; as the stem, leaves, 

 flowers, seed-vessels and seeds, and even in the interior of vessels. 

 Cotton is the hair surrounding the seeds of Gossypium herbaceum. 

 Hairs are developed occasionally to a great extent on plants exposed to 

 elevated temperatures, as well as on those growing on lofty mountains. 

 When occurring on the organs of reproduction, they seem to be con- 

 nected with fertilization, as the hairs on the style of Goldfussia or 

 Ruellia, and the retractile hairs of Campanula. Different parts of plants 

 are transformed into hairs; as may be seen in the flowering stalks of 

 Rhus Cotinus, and in the calyx of Composite. 



60. Names are given to the surfaces of plants according to the 

 presence or absence of hairs, as well as the nature of the hairs which 



Fig. 83. Scale or scaly hair, from leaf of Hippophae rhamnoides. 



Fig. 84. Peltate hair' of Malpighia, pp, arising from epidermis, e. y, The gland which com- 

 municates with the hair. 



