Xxiv OUTLINES OF 



or resinous matter, but more frequently dry. They are generally few in number, often 

 definite in their position and form, and occur chiefly on the petiole or principal veins 

 of leaves, on the branches of inflorescences, or on the stalks or principal veins of 

 bracts, sepals, or petals. 



2. Minute raised dots, usually black, red, or dark-coloured, of a resinous or oily 

 nature, always superficial, and apparently exudations from the epidermis. They are 

 often numerous on leaves, bracts, sepals, and green branches, and occur even on petals 

 and stamens, more rarely on pistils. "When raised upon slender stalks they are called 

 pedicellate (or stipitate) glands, or glandular hairs, according to the thickness of the 

 stalk. 



3. Small, globular, oblong or even linear vesicles, filled with oil, imbedded in the 

 substance itself of leaves, bracts, floral organs, or fruits. They are often very nu- 

 merous, like transparent dots, sometimes few and determinate in form and position. 

 In the pericarp of Umbelliferce they are remarkably regular and conspicuous, and 

 take the name of vitlce. 



4. Lobes of the disk (137), or other small fleshy excrescences within the flower, 

 whether from the receptacle, calyx, corolla, stamens, or pistil. 



Chap. II. Classification, oh Systematic Botany. 



176. It haa already been observed (3) that descriptions of plants should, as nearly 

 as possible, be arranged under natural divisions, so as to facilitate the comparison of 

 each plant with those most nearly allied to it. The descriptions of plants here al- 

 luded to are descriptions of species ; the natural divisions of the Flora refer to na- 

 tural groups of species. 



177. A Species comprises all the individual plants which resemble each other suf- 

 ficiently to make us conclude that they are all, or mag have been all, descended from a 

 common parent. These individuals may often differ from each other in many striking 

 particulars, such as the colour of the flower, size of the leaf, etc., but these particulars 

 are such as experience teaches us are liable to vary in the seedlings raised from one 

 individual. 



178. When a large number of the individuals of a species differ from the others m 

 any striking particular they constitute a Variety. If the variety generally comes 

 true from seed, it is often called a Race. 



179. A Variety can only be propagated with certainty by grafts, cuttings, bulbs, 

 tubers, or any other method which produces a new plant by the development of one 

 or more buds taken from the old one. A Race may with care be propagated by seed, 

 although seedlings will always be liable, under certain circumstances, to lose those 

 particulars which distinguish it from the rest of the species. A real Species will 

 always come true from seed. 



180. The known species of plants (now near 100,000) are far too numerous for the 

 human mind to study without classification, or even to give distinct single names to. 

 To facilitate these objects, an admirable system, invented by Linnteus, has been uni- 

 versally adopted, viz. one common substantive name is given to a number of species 

 which resemble each other more than they do any other species ; the species so col- 

 lected under one name are collectively called a Genus, the common name being the 

 generic name. Each species is then distinguished from the others of the same genus 

 by the addition of an adjective epithet or specific name. Every species has thus a bo- 

 tanical name of two words. In Latin, the language usually used for the purpose, th e 

 first word is a substantive and designates the genus; the second, an adjective, indi- 

 cates the species. 



181. The genera thus formed being still too numerous (above 6000) for study with- 

 out further arrangement, they have been classed upon the same principles, viz. genera 

 which resemble each other more than they do any other genera, have been collected 



