30 Ttie Tismes of Plants. 



which after a time coalesced and formed a united whole ? Neither 

 of these views are strictly true ; they could not originally have been 

 a perforated mass, because we often find between two cells, a 

 double wall with a space between, which of course could never 

 have happened if this view were true. The fact is, the first germ 

 of all plants consists of only one cell. This cell, after enlarging 

 and attaining to a certain size, becomes split into two ; that is, a 

 cell-wall is formed across the middle of the cell. These two cells 

 again go on increasing till each of them divides into two again, and 

 so on. This is the way in which the growth of plants is effected. 

 To give some idea of the smallness of cells, I may mention that it 

 has been calculated that in an ordinary plant there are 1728 

 millions in a cubic inch. I have said that the growth of ])lants is 

 effected by the division of each cell into two after it attains a 

 certain size. In this manner a solid tissue is formed, that is, all 

 the cells are joined together. But in some plants as soon as the 

 new cell-wall has divided the old cell, the two new cells thus 

 formed separate and become independent of each other. In this 

 way the tissue, which is the name given to a fabric composed of 

 cells, is loose and disconnected. The forms of cells vary con- 

 siderably, according to their position. Thus when they are free 

 and independent of each other, they are more or less spherical; 

 when they press upon each other they become many-sided. In- 

 deed, the variety of their forms is so great, that the hairs with 

 which many leaves or other parts of a plant are clothed, are merely 

 cells which have grown out from their original position within the 

 leaf. 



Besides these cells, however, there also are elongated cells, 

 properly called vessels. These vessels are thus formed : — The cells 

 stand one above another in a long line, and by degrees the wall 

 which separates the cells from each other becomes thinner or 

 entirely vanishes, and thus we have a long line of cells open all 

 through. These are the vessels. They are naturally of a more 

 or less cylindrical form, just as the cells are as a rule spherical. 

 The inside of the vessel is variously marked with a kind of thicken- 

 ing matter, which in some plants takes the form of a continuous 

 spiral fibre creeping up the vessel, in others of mere dots studded 

 about upon the vessel. This latter is chiefly to be seen in woody 

 plants. Thus far, then, we have seen the general formation of 

 which plants are built up — viz., of cells and of vessels ; what we 

 have now to examine is the chemical properties of these cells, and 

 the manner in which water is circulated throughout the whole 

 plant. The substance which forms the cell-wall is called cellulose. 

 This substance, when pure, is a ternary compound of carbon, 

 hydrogen, and oxygen ; and as these last two, hydrogen and 



