20 PLANT LIFE 



with food materials, it multiplies rapidly. 

 When an individual has reached a certain 

 size it divides into two, and this process being 

 repeated in the various individuals of a colony 

 the Pleurococcus spreads rapidly over the 

 surface of the damp wood. Furthermore, 

 the individual plants withstand desiccation 

 without dying, and in this condition they are 

 carried by currents of air to fresh spots where 

 new colonies can be started. 



But to return to Chlamydomonas. Its 

 second feature of importance, from our present 

 point of view, consists in its greenness. 



As we have seen, the green colouring matter, 

 or chlorophyll, is not diffused through the whole 

 protoplasm, but is restricted to one or more 

 (in this plant, one) definite and specialised 

 masses or corpuscles, each of which constitutes 

 a chloroplast. The part which the chloroplast 

 plays in the cell * is that of utilising the energy 



1 CELL. This is the term commonly used to denote the 

 unit of a living organism, though, unfortunately, it is 

 not always used in the same sense by different writers. 

 In this book it will be taken to denote a mass of protoplasm 

 (whether enclosed in a cellulose membrane or not) which 

 is dominated by a single nucleus. This protoplasmic mass 

 is commonly, but not necessarily, separated by a cell 

 membrane from other similar ones in the cell -aggregates 

 which together constitute the bodies of larger plants. 

 A plant may thus consist of (1) a single cell; (2) a number 

 of coherent cells, each more or less delimited from the 

 rest by a membranous envelope or partition wall; (3) a 

 number of coalescent cells, consisting of protoplasmic 

 units, each containing one nucleus, but the units not 

 separated from each other by cell walls. Such a cell colony 



