MANUAL OF AGPJCULTUEE. 237 



features. ''Joints" are the lines of fracture seen dividing rock 

 masses into separate lumps or blocks, and wliich facilitate the 

 quarrying of [them. "Faults" are such fractures oF the strata 

 series as raise or depress the level of the strata on one side of 

 such faults above or below that of the strata on their other side, 

 and thus break the continuity of stratification. 



Chapter IV. — Of Botany. 



Of the science of Botany, physiological botany is that one of 

 its departments which most concerns the practical agriculturist, 

 treating, as it does, of the different organs of plants, and theii- 

 respective functions. The classitication of plant life is a field of 

 study too extensive for his time and opportunities. But as all 

 the British cultivated plants are included in a very few " orders," 

 the comparative slightness of their physiological variations ren- 

 ders his acquisition of this branch so much the easier by its 

 approximation to a uniform applicability. 



A normally developed plant consists of four different organs, 

 viz., root, stem, leaves, and fiowers, — the first three being nutritive 

 organs, and the fourth that of reproduction. They are alike 

 modifications of one structure, for the fundamental structure of 

 all plant forms is the simple cell. Cells are minute, round, 

 bladder-like vessels, which cohere and form cellular tissue, 

 named imrcncliyma. They have their origin in a thin mucilagin- 

 ous compound called 'protoplasm, which is considered the seat of 

 life. A small germ, termed a nucleus, appears in the protoplasm, 

 which presently, with some of the protoplasm, gets enclosed by a 

 species of sac or covering, and this constitutes a cell. Increasing, 

 the nucleus seems to be divided, and the cell-wall closing round 

 either portion, forms two distinct cells. And so on indefinitely. 

 This cell-wall or envelope is formed of a substance termed cellu- 

 lose, the composition of which will be subsequently given. 

 Active cells, besides containing protoplasm and nuclei, for the 

 purposes of increase, and also their several characteristic contents, 

 have, when situated at the exterior portions of plants, cliloropliyll 

 as well, which is their green colouring matter, and has the pro- 

 perty, when it is acted upon by sunlight, of assimilating certain 

 elements from the atmosphere. The shells of nuts and other 

 seeds are composed of hard solidified cells ; the roots of turnips, 

 potatoes, &c., almost entirely of juicy cells. The cell-walls or 

 coverings of dilierent |jlant groups have characteristic marks, 

 whether dotted, barred, reticulated, or with spirals or other 

 quaint devices. Cells cohere by means of connective tissue, 

 supposed to be secreted from their walls. " Intercellular" canals 

 are the spaces formed where cells do not adhere on all sides ; and 

 they serve for circulating air through the plant structure. Fibres 



