\0h ANATOMY AND PHYSIOLOGY Of 



B.-THE CELL AS AK ORGAIST OF PROPAGATIOISr. 

 a. The Multiplication of Plants hy Division, 



Multiplication by division occnrs nnder different forms according 

 to the lower or higher stage of organization of the plants ; for the 

 lower it is, the more does the individual cell possess the power of 

 independently producing a new vegetable, whether by simple 

 division or by the formation of a bud ; while the higher the or- 

 ganization of the entire plant stands, the more does the capabihty 

 of maintaining an independent vitality leave the individual cells 

 and become committed to smaller or larger assemblages of cells, 

 which must become developed into an organ of complicated 

 structure, before their separation from the parent plant, to ensure 

 their growing up into independent plants 



Multiplication of plants by division of every individual cell is 

 a very common phenomenon in the lowest forms of Algse. In the 

 geneiality of cases, the dividing cell parts into two, more rarely 

 into four cells, in which again the same process of multiplication 

 may be repeated. This is of universal occurrence in the uni- 

 cellular Algae, e, g., in the Diatomaceae, DesmidiacesB, &c. ; after 

 the division, the newly-formed cells either separate from each 

 other or remain joined together in colonies arranged in rows or 

 flat layers, more or less firmly connected by a mass of mucilagi- 

 nous matter, thus forming a transition towards the plants com- 

 posed of numbers of cells. 



The same process is repeated in the many-celled Algae, for 

 example, in the Oscillatorieae ; in the first instance, growth of the 

 single individual is the result of the process of division of the 

 cells in these plants, but the extraordinary readiness with which 

 they break up into separate pieces, or, as in Nostoo, the single 

 cellular filaments separate fi^om each other by solution of the 

 connecting mucilage, together with the power of the single pieces 

 to grow up again into new plants, give great facihty to the mul- 

 tiph cation of the individuals by division of their cells. 



The capability of multiplying in tliis way by unceasing divi- 

 sion of the cells, appears to be unlimited in many lower plants, 

 such as the Diatomacese, Oscillatorieae, &c ; at all events, any 

 other mxode of propagation has been either rarely or not at all 

 discovered in them; in other cases, however, and especially in the 

 Desmidiacca? {see Ealfe' ''British Desmicliem,'' 5) this division is 

 confined within definite limits. After a series of divisions have 

 taken place, this process ceases, and the formation of spores 

 begins. 



Among the plants possessing a thallus composed of numerous 

 cells, the development of single cells or groups of cells into inde- 

 pendent plants occurs chiefly in the Lichens, where very frequently 

 the layer composed of globular cells breaks up, by the cells fall- 

 ing apart into the form of powder (gonidia, lagerkeime), either 



