78 'Ve(jetable Flujsiolorjy. 



would grow. Thus in tlie same length of time that the first cell 

 occupied in dividing into four, these four may repeat the process 

 and- produce sixteen ; then if each of these divides in the same 

 way, the next subdivision, effected in the same space of time, 

 will produce sixty-four, and so on. 



It is exactly by this kind of operation that all vegetable struc- 

 ture grows, that all parts of plants increase in size : namely, by 

 a division of existing cells into two, four, or more parts, each of 

 which may swell up to the size of the parent-cell by which it 

 is produced. And since all vegetable structure is of this cellu- 

 lar nature, and no plant can exist except by origin from a cell 

 of this kind, having the power of increasing itself in this way, 

 of course the ideas that are sometimes entertained of vegetables 

 springing up spontaneously, without having had parents like 

 themselves, are altogether erroneous, for nothing but a living 

 plant can produce a reproductive cell capable of originating a 

 new course of growth of this kind. 



If, however, we wish to understand thoroughly the mode of 

 increase and growth of plants, we must go even deeper into the 

 character of the cells and inquire hoio they divide when giving 

 birth to new ones. This can be observed more easily in plants 

 composed of cells larger than those of Protococais, but still 

 small enough and transparent enough to allow us to see into the 

 intei'ior with the microscope. In sunny weather the surface of 

 ditches and stagnant pools is usually more or less coated with a 

 yellowish green froth or scum. If we take a little of this and 

 place it in a glass of clear water we see that it is composed of num- 

 berless extremely fine gi'een filaments, like fibres of unspun silk ; 

 if we place these filaments under the micioscope we find that 

 they are hollow, and, in fact, are formed of little tubular cases 

 or cells joined end to end, so as to form a string of cells. The 

 cells of such filaments present a great variety of beautiful ar- 

 rangements of the cells and their contents, in the different species 

 of these plants (called Confervoids), which are very numerous. 

 Some are simple, thread-like rows of cells ; others are branched. 

 Some are filled with green substance ; others have the green 

 substance arranged in spiral lines or in a network on the inside 

 of the wall of the cell. Many of them are of considerable dia- 

 meter, so that the processes taking place in the inside of the 

 cells are very easily observed under the microscope, and thence 

 enable us to ascertain exactly how the cells of plants increase in 

 number by dividing. 



A common group of Confervas, called Spirogyrce, have the 

 green colouring matter in the form of one or more spiral lines or 

 bands lying upon the inside of the wall of the cell. Wiien we 

 place one of these filaments under the microscope, we see the 

 cells (which are of the shape of the stones in a column) adjoining 



