94 BOTANY 



arose. While plants had only a unicellular body, the 

 division of the cell caused the appearance of a new in- 

 dividual. In fact, the individual was the same thing as 

 the cell. But when the cells failed to separate this 

 ceased to be the case, and the individual plant became 

 identified with the chain of cells. Division of a cell so 

 added another link to the chain, but it did not produce a 

 new individual. For a time the simple method of re- 

 production by cell division was replaced by the break- 

 ing of the chain into a number of segments, each of 

 which grew into a new filament like the first. This 

 method of reproduction is shown now by certain blue- 

 green algae and by many fungi. 



These simple methods, however, led to the production 

 of comparatively few offspring. A larger number 

 became desirable if a species was to hold its own in the 

 competition with its neighbours for what the surround- 

 ings afforded, particularly as the life of any individual 

 was but short. So there arose in the plant body special 

 cells, usually in great numbers, which could be detached 

 and give rise to new individuals. Various forms of 

 these cells are still met with ; some with no membrane, 

 able to swim about by means of little protoplasmic 

 thread-like outgrowths, known as cilia, which by rapid 

 vibrations set up currents in the water ; some motion- 

 less and well protected by firm cell walls, so as to be able 

 to resist heat or cold, and even some degree of drying 

 up. Such little specialised reproductive cells are now 

 generally called gonidia. They are still produced in 

 various ways and usually in very large numbers by 

 many of the seaweeds and another group related to 

 them the fungi. This showed a great advance in the 

 spread of the species, as each of the large number 

 produced could give rise to a new plant. 



But such rapid reproduction tends to weaken the race, 

 and no doubt it told its tale in the ancient times. It 



