17 



CHAPTEE II 



THE DIFFERENTIATION OF THE PLANT-BODY 



THE primary needs of a complex plant are the same as those 

 of a single protoplast, the greater size of the former involv- 

 ing however a more elaborate method of supplying them. 

 In multicellular plants we consequently meet with a consider- 

 able degree of differentiation of structure. Each protoplast, 

 which is one of the units of the colony, has originally the 

 same properties as the unicellular plant. With increase 

 of number in the plant- body, and with the consequent 

 increase of size, a certain division of labour soon makes 

 its appearance, and particular groups of cells develop one 

 property more than the others. A specialisation of powers 

 is very quickly apparent, and we can recognise masses of 

 cells devoted to the discharge of one function, others 

 to that of another, and so on. Such limitations of the powers 

 and properties of the individuals have for their object the 

 well-being of the community of which those individuals 

 are constituents. 



Various groups of plants show this specialisation of 

 function or differentiation of structure in very different 

 degrees, any particular development having a special 

 reference to the habitat or the mode of life which is 

 characteristic of the community in question. A plant-body 

 which takes the form of a long filament or a plate of cells 

 shows little differentiation beyond the formation of a 

 vacuole in each protoplast. The setting apart of special 

 cells for purposes of reproduction is generally the first 

 specialisation which takes place. 



As soon as the cells of the plant begin to divide in 



c 



