110 PLEUROCOCCUS. [CH. VIII 



stems which float away and make new plants. These 

 forms of reproduction are precisely the same as the 

 artificial continuance of species practised by gardeners, in 

 making cuttings. In none of these cases does the question 

 of sex enter into the problem. The river-weed, Elodea, 

 which has spread in this way throughout the rivers of 

 England, consists entirely of female plants ; and the same 

 thing might have happened if the original parent plant had 

 been a male. For this reason these modes of reproduc- 

 tion are classed together as asexual or vegetative. 



It will be seen later that many plants produce separate 

 and special cells which serve for asexual reproduction. 

 Such cases help us to realise that asexual reproduction 

 is quite as mysterious and wonderful as sexual reproduc- 

 tions. The essence of the thing is that in a single cell 

 there should be locked up the potentiality of a future 

 plant, i.e. that a single cell should be able to grow into 

 a perfect plant; and that this should be possible is 

 equally wonderful, whether the new growth originates in 

 an asexual reproductive cell or an ovum. 



The difference between the two is that the egg-cell does 

 not normally develope until it has been fertilised (i.e. 

 infected or stimulated) by being fused with the male 

 element, whereas the asexual reproductive element re- 

 quires no such treatment. 



Pleurococcus. 



When an organism is simple in structure, when for 

 instance it consists of a single cell, asexual reproduction 

 may be, as far as observation is concerned, a perfectly 



