BOTANY. Y 



Stomata occur on all portions of the plant, especially in the green parts. 

 They rarely exist in the Cellulares or in pale parasites, and never in roots and 

 etiolated plants. The number varies greatly in different portions of the same 

 plant, being, however, greatest on the under side of leaves exposed to the air, 

 and 3^et sometimes entirely wanting on the upper surfaces. In floating leaves 

 the stomata only occur on the upper surface. The following table ex- 

 hibits the number of stomata to the square inch on the leaves of several 

 plants : 



Various processes ai^e seen at times on the surface of the epidermis by the 

 outward enlargement or projection of some cells. When these are more con- 

 siderably elongated they constitute haii-s ( pili or villi), and are covered by the 

 cuticle as by a sheath. They are either lympliatic or glandular, the latter 

 distended at the^ base or apex, to receive certain secretions. In respect to 

 position, hairs are erect or oblique, or else lie flat along the surftice {ad- 

 pressed) ; when attached by their middle, they are 2)eltate. They may be 

 composed of a single cell, which is either simple, forked, or branched ; or else 

 of several cells, which are either placed end to end, as in moniliform hairs, oi- 

 united laterally into a compound cone, compound hairs, or branched. When 

 several hairs proceed from a common centre, they are said to be stellate or 

 radiated. These, when close pressed together, so as to form a discoid ex- 

 pansion, constitute a scale or scurf {lepis) ; the surface is then said to bo 

 lepidote. This character is well seen in Ilippophae. A chaffy substance, 

 surrounding the base of the leaves of ferns, consisting of elongated flattened 

 cells, is constituted by ramenta or r amentaceous hairs : a similar substance 

 in palms is called reticulum or inattula. Prickles [aculei) are hardened 

 hairs, connected solely with the epidermis. These differ from thorns, 

 which are stunted branches, and are connected with the wood. Setoi are 

 bristles or stiff" hairs ; the surfaces on which they occur are said to be setose 

 or setaceous. 



Hairs, in regard to their form, are clavate, or club-shaped, Avhen they 

 expand gradually from -the base to the apex, or are thickened at the apex ; 

 when there is a distinct rounded head, they are capitate : when they have 

 slight projections on the surface, they are scabrous ; hooked or uncinate, 

 wlien with a hook at the apex turned downwards ; barbed or glochidiate, with 

 two or more hooks around the apex ; peltate, when attached solely in the 

 middle; ciliate, when surrounding the margin of leaver. 



Hairs are found on various parts of plants, even in the interior, and 



7 



