IMPORTANCE OF THEORY, 131 



works numerous illustrations of the importance 

 of theory in the investigation even of matters 

 of detail. Writing of the trimorphic Lythrum 

 salicaria, he said, "The existence of the three 

 forms was first observed by Vaucher, and sub- 

 sequently by Wirtgen ; but these botanists, not 

 being guided by any theory or even suspicion 

 of their functional differences, did not perceive 

 some of the most curious points of difference 

 in their structure." 1 MM. Boitard and Corbie, 

 in their study of pigeons, had seen and recorded 

 many facts which they could not use, simply 

 from lack of a theory. They had stated that 

 when they crossed certain breeds of pigeons, 

 birds colored like the Columba livia, or the 

 common dove-cot, were almost invariably pro- 

 duced. 2 Darwin gave significance to these facts 

 and many others by the theory of descent. 



In spite of his unusual power of seeing facts 

 apparently unconnected with the subject under 

 investigation, and his persistent habit of record- 

 ing results, whatever they might be, Darwin 

 himself, sometimes " not foreseeing the result, 

 did not keep a memorandum of all the facts," 

 which would afterwards have proved useful. 



1 Different Forms of Flowers on Plants of the same 

 Species, p. 138. 



2 Variation of Animals and Plants under Domestication, 

 Vol. II. p. 14. 



