224 THE GARDENER. [May 



indiscriminately found in any of these soils, especially if they have 

 been in any way decomposed or intermixed : The elevation of land 

 above the level of the sea, and, within certain limits, the latitude of 

 the countries in which they are found, where the daily average annual 

 amount of sun-heat during the season of growth of plants is above 

 the degree of heat necessary first to start them into growth, and 

 sufficient to enable them to complete their full growth, and which in 

 the case of annual plants must necessarily be above freezing-point, or 

 they could not germinate: The relative situation of islands to contin- 

 ents or mainland : The presence of vast tracts of land covered with 

 fresh or salt water, and the currents in the latter : The state of the 

 atmosphere, its dryness or moisture, its currents of wind, its chemical 

 composition — some plants delight in an atmosphere charged with 

 chloride of sodium or sea-salt which would be destroyed by an 

 application of such salt to their roots : The amount of sunlight, often 

 as important as sun-heat, and, in fact, as we approach the poles, re- 

 placing its want : The power of the chemical or actinic rays of the 

 sun : The inherent vital power in the plant itself to resist destructive 

 agencies. Upon some or other of the above or similar secondary 

 causes, with here and there anomalous exceptions, the habitat of 

 plants may be said to depend. 



AVe must now proceed to the main part of our subject — the plant 

 — and try to elucidate some of its characteristics. 



Each plant is an aggregation of cells ; each cell consists of a little 

 transparent spherical sac or globe ; the outer membrane enclosing it is 

 made of cellulose, which, by the by, is insoluble in water, containing 

 in it liquid or viscid granular matter, sometimes called the primor- 

 dial utricle, or protoplasm, made of carbon, oxygen, hydrogen, and 

 nitrogen, and some sulphur and phosphorus ; and within the proto- 

 plasm is a nucleus. These cells grow either by internal or external 

 growth, or by division of the cell into two cells (by plant growth 

 is meant either formation of new cells, or increase of cells al- 

 ready made, or thickening of cell walls). Each cell nourishes 

 another cell ; and where there is no pressure the spherical or globe 

 shape will remain ; but where there is pressure this appearance is 

 soon lost sight of, and it then assumes various forms and shapes, and 

 is called cellular tissue. The outer covering of all plants is called the 

 epidermis, and is in reality cellular tissue. As a consequence of cell 

 growth, each plant has the power of reparation of injuries done to it. 



Eor convenience of classification, each plant will be found to belong 

 to some collection of plants called a species, supposed to have had, 

 in monoecious plants, a common ancestor, or in dioecious plants, a 

 pair of ancestors ; and each species will belong to a group of one or 



