12 



AUAIYTICAL CLASS-BOOK OF BOTAJJY. 



more or less elongated. Sometimes they are formed by 

 tte prolongation of a single cell, as in the Cabbage, fig. 

 15 ; and at others, they consist of several cells variously 

 united and combined. Sometimes the cells are united 

 end to end, in a linear series, as in the Snapdragon, fig. 

 9, where also they are jointed. In the Marvel of Peru, 

 fig. 7, the hair cells are strung together like beads. A 

 unicellular hair is sometimes branched or expanded into 

 rays, as in Alyssum. In fig. 3, at o, such a hair is seen, 

 while in the transverse section, at h, its stellate form is 

 more apparent. Fig. 14 represents a section of the epi- 

 dermis from the Cabbage much magnified, showing full- 

 grown hairs, and others in various stages of protrusion. 

 The oval openings are stomata. At fig. 16 is the Gar- 

 den Borrage, which is thickly invested with long and 

 shaggy hairs. 



81. Pubescence is the term used to express the dif- 

 ferent kinds and degrees of hairyness on the surface of 

 plants. These characters are so uniform as to be of 

 considerable importance in specific distinctions. The 

 surface is said to be 



(1) Hispid, when clothed with rigid hairs or bristles — 



(2) Hirsute, with long, coarse, spreading hairs — 



(3) Pubescent or downy, with soft, short hairs — - 



(4) KouGH, with short, stiff hairs — 



(5) ViLLOSE, clothed with long, coarse and shaggy 

 hairs — 



(6) ToMENTOSB, matted and entangled together in 

 cotton-like masses, as in theLeaf of several Poplars; and 



(7) Lanatb, woolly, as in the leaf of Mullein. 

 Many other terms are used to express different varieties 



of pubescence, as Silky, Velvety, Arachnoid, like a 

 spider's web, and Ciliatb, fringed like an eyelash. 

 Hairs are found on the leaf, stem, root, and almost every 

 part of the plant. They invest many seeds, and are fre- 

 quently hooked, jointed, or barbed. 



82. Glands are epidermal appendages that contain and 

 discharge various solids and liquids, such as oils, sugar, 

 resins and acrid juices. Sometimes they are embedded 

 in the substance of the leaf, causing it to appear dotted, 

 as at fig. 12. The Lemon also has a glandular leaf. 

 Glands are deposited in the notches of the leaf, as in the 

 Bay-leaved Willow, or on the leaf-stalk, as in the Cherry. 

 There is a gland at the base of the petals in the Butter- 

 cup, and a pair in those of the Crown-Imperial, fig. 1 1 , 

 one of which was overlooked in the delineation. Glands 



Varieties. Describe. Pubescence. Wben IIL^pid — Hirsute — Pubescent — 

 Eougli — Villose— Tomentoso — Lanate? Eeverse tbe last seven questions. 

 When lilie a spider's web, -what called? Like an eyelasb, -what? On what 

 parts are hairs found. Glands. What contain? Where fonnd? Instances. 

 Elov&ted on hairs. Stings. Describe. Instance. What liite ? Prickles. In- 



are sometimes elevated on hairs, as in the Spider-wort 

 and the Snapdragon, fig. 9. A beautiful instance of this 

 arrangement is seen in the Sundew, fig. 10. In a state 

 of nature, the glands give to the whole plant the appear- 

 ance of being covered with little pellucid dewdrops. 

 Such hairs are termed Glandular Hairs. The gland, 

 instead of being borne on the summit of the hair, is 

 sometimes fixed at the base. 



83. Stings consist of rigid, tubular hairs, fixed in a 

 roundish glandular base, which secretes an irritating 

 liquid. On the least disturbance of these points by the 

 hand, the liquid which they contain is injected into the 

 skin, and a stinging sensation ensues. The common 

 Nettle is a familiar instance of this habit. There is a 

 striking analogy between these and the stings of animals. 



84. Prickles are strong and indurated protrusions of 

 the epidermis, having a sharp point, which is often also 

 curved, as we see in the Raspberry and the Rose, fig. 13. 



85. The Intercellular System. — By a reference 

 to fig. 17, you will see that there are between most of 

 the cells, and especially those of the lower strata, certafn 

 irregular spaces, varying greatly in size and form. These 

 constitute what is called the Intercellular System. 

 They are in some cases, without doubt, caused by imper- 

 fect cohesion, and are thus in some degree the effect of 

 accident ; but from the fact of their containing air, and 

 also being connected with the stomata or breathing 

 pores, it may be inferred that they have their fixed and 

 essential uses in the vegetable economy. This is more 

 apparent in aquatic plants, where often the intercellular 

 spaces are greatly extended, and apparently constructed 

 with as much care and nicety as any other organ. By 

 this means, their leaves and stems are not only rendered 

 buoyant, and kept in a floating position, but are interiorly 

 supplied with air, which is necessary to their vital opera- 

 tions. An instance of this habit may be seen in the 

 marine plant, fig. 7, Plate III. where certain portions 

 of the stem are greatly inflated by the enlarged intercel- 

 lular spaces. 



CHAPTER VIII. 



PEOGEESSITE DEVELOPMENT 



86. By a countless multiplication of cells in a plant 

 of the higher orders, a structure is developed composed 

 of distinct parts or organs. You have already become 



stances. What do tbe spaces between the cells constitute f With what organ 

 connected? Whatcontain? In "what plants very large? Howuseful? Point 

 them out in fig. 17. 



General subject To what does It lead ? 



