304 THE LIFE OF THE PLANT 



Moreover, we differentiate between babies and adults, 

 youths, mature and old men ; and these conceptions are 

 entirely in accordance with reality, otherwise they 

 would not have arisen in our mind. It does not, how- 

 ever, follow that they must be applied without exception 

 to all cases. Nobody would ever think of affirming 

 that questions must or can be decided, in any and every 

 case, such as : Have we before us an adult or a youth, 

 a grown-up person or an old man ? and so on ; and yet 

 it is with such problems that systematists struggle 

 when they have to decide whether a doubtful species 

 is to be considered a species or a variety. Species and 

 variations are clearly differentiated in most cases ; 

 but it does not follow that they should be two categories 

 essentially different ; on the contrary, the difference 

 between them is entirely one of quantity. They are 

 two quantities passing gradually into one another : 

 at one extreme we have slight individual variations, 

 succeeded by sub-varieties, then obvious varieties, 

 doubtful species, and, lastly, good species* In a word, 

 the only logical solution to this problem of species 

 and varieties, so full of contradictions, consists in the 

 acceptance of Darwin's formulae: 'A variety is an in- 

 cipient species ' ; * a species is a strongly-marked variety ' : 

 just as a child is an undeveloped man, and a grown-up 

 man is a developed child, nor can any line of demarcation 

 be drawn where the child ends and the man begins. Let 

 us carry our comparison further. Supposing that a being 

 of some kind with a very short period of existence (a may- 

 fly, for instance) were to raise the question whether a 

 grown-up man develops from a child, or whether they 

 are both quite independent beings. It would be 

 impossible for our imaginary being to see this trans- 

 formation because of the shortness of its own existence ; 



1 In fact, while systematists were able formerly to end their classifica- 

 tion with species, to-day four subdivisions more are admitted within the 

 limits of the species. 



