INTRODUCTORY REMARKS. 



27 



Gardening as a practical art must be learnt 

 practically; but the more practice is learned 

 with and guided by knowledge and trained 

 intelligence the better will the practice be. 

 Intelligence may be cultivated in various ways, 

 but it stands to reason that the intelligence of 

 the gardener should be exercised in the study 

 and consideration of the objects he is expected 

 to deal with. It is not desirable, even if it were 

 possible, that a gardener should be an expert in 

 all, or even in any one, of the branches of know- 

 ledge before mentioned, but he should certainly 

 have such a general acquaintance with them as 

 will enable him to appreciate their bearing upon 

 his daily practice. This will permit him to avail 

 himself of the resources which the scientific man 

 is constantly placing at his disposal, and will 

 enable him not only to maintain the standard 

 of horticultural excellence, but to promote its 

 advance — an advance that practice of itself will 

 never enable him to accomplish. 



The Cell and its Contents. 



Like all living creatures plants grow from 

 very small beginnings. The cell of which we 

 are about to speak is not the actual beginning, 

 but, for convenience sake, we here take it as 

 our starting-point. A cell in appearance is a 

 very simple thing (figs. 9, 10, 11), though it is 

 usually so small as to be 

 invisible to the naked eye. 



Fig. 10. 



Isolated Cells (figs. 1 and 2) with and (fig. 3) 

 without Nuclei— highly magnified. 



Fig. 12.— Elder Pith, con- 

 sisting of aggregations 

 of Cells— magnified. 



But in a piece of elder-pith (fig. 12), or, better 

 still, in the pulp of the orange, it is easy to 

 see that the spongy substance^ of which either 

 consists is made up of cells. They look like 

 little bags or bladders of membrane, containing 

 fluid and other contents. The complete cell 

 consists of a membranous bag, or cell-wall as 

 it is called, and of various contents, the most 

 important of which is a viscous substance, found 

 invariably in all living cells, and which is called 

 protoplasm. This is colourless, and hence is not 

 easily seen even under the microscope till its 

 presence is made obvious by the addition of acids, 

 which cause it to shrink and separate from the 

 cell-wall, or by the use of colouring matters 

 (dyes), which alter its texture and colour, and 



Fig. 13.— Protoplasm in motion, 

 in the direction of the arrows 

 — VallisneHa 



render it conspicuous. Thus a solution of hema- 

 toxylin (the colouring matter of logwood) stains 

 both the cell-wall and its contents, but in dif- 

 ferent degrees. Carmine stains the protoplasm 

 and its contents, but leaves 

 the wall uncoloured, or 

 only faintly tinged. Nitric 

 acid and ammonia stain 

 the protoplasm a bright 

 yellow. To the chemist 

 this change of colour indi- 

 cates the presence of nitro- 

 gen. 



The cell-wall consists of 

 a substance known as 

 cellulose, a substance con- 

 taining no nitrogen, but 

 nearly allied to starch, 

 and, like it, coloured blue 

 when treated with iodine 

 and sulphuric acid. In a 

 young condition, and when 

 not thickened by deposits 

 on its inner surface, it 

 allows of the passage of 

 watery fluids through its 

 texture into the interior 

 of the cell. 



The protoplasm is in all 

 ways the most important part of the cell, the 

 bag or cell-wall which incloses it being merely 

 of a protective nature. The protoplasm is sen- 

 sitive to impressions, now contracting, now dif- 

 fusing itself, according to circumstances, and 

 often endowed with 

 powers of motion (fig. 13). 

 Moreover, it can, and 

 does sometimes, exist by 

 itself. The living cell- 

 wall, on the other hand, 

 cannot maintain an inde- 

 pendent existence. If it 

 occurs, as it does some- 

 Ypy^ J\^ M times, without proto- 

 Jllllljl f-^JSj| plasm, it is as a mere 

 dead shell endowed with 

 physical, but destitute 

 of vital, properties 



Even 

 constituted of protoplasm 

 and cell-wall has, or may 

 have, in the protoplasm, at some period of its 

 existence, a small, relatively hard, highly-refract- 

 ing body called the "nucleus" (figs. 9 and 10), 

 which, when the cell is dividing, undergoes a 

 series of most remarkable changes and plays a 



Fig. 14.— Section across Wood- 

 cells, showing concentric 

 layers of woody matter sur- 

 rounding a central cavity— 

 Scolopendrium. 



living cell thus 



