56 THE VEGETABLE KINGDOM. 



If on plants, strip the stem with your fingers, and in the 

 same way drop the gelatinous mass in water. Let it settle, 

 and the little plants will flourish and remain long enough 

 for you to study, not only their lovely forms, but also their 

 manner of propagation, which is threefold. They multiply 

 by self-division, by conjugation, or by zoospores. 



The most common way is this : when a simple cell has 

 come to its full growth, a partition forms in the middle ; 

 the cell gradually separates into two halves, each of which 

 speedily becomes a perfect species of Desmidiacea. 



The increase by conjugation, observed particularly in 

 Closterium and Cosmarium, takes place thus : two fronds 

 approach each other, and the outer cell-wall of each splits 

 and throws out a connecting-tube which joins them together. 

 Through this tube the contents of one cell is poured into 

 the other, and mixing with the endochrome of the receiving- 

 cell, forms a body called sporangium, which is afterwards 

 set free by the breaking up of the parent cell. 



Multiplication by zoospores has been observed in Cosma- 

 rium, Pediastrum, and many others. The endochrome 

 divides into a number of granular particles called gonidia, 

 which escape through the cell- wall, and develop into per- 

 fect cells. 



Or they are ciliated and have a spontaneous movement, 

 both in the parent cell and out of it, when they are called 

 zoospores. 



CONFERVA. ZYGNEMA. 



This is mounted for the microscope, as an example of 

 conjugation amongst the Confervacese. 



Confervaeese are those plants which form the green or 

 brown scum on ponds and ditches, and the long green, 

 silky threads, that float in running water. Most beautiful 

 are their ribbon-like filaments of varied pattern, and most 

 useful their life on the stagnant water, which they purify 

 by absorbing the noxious gases, and giving out the life-sus- 

 taining oxygen. 



Looking at this scum for the first time will probably 

 surprise us as much as anything. It does seem so won- 



