32 THE WAY OF A TROUT WITH A FLY 



from mechanical considerations as to the structure and 

 wearing power of the fly, shape is of very secondary 

 consequence. 



IX 



TONE 



One theory of some who do not believe in the colour vision 

 of trout is that it is tone only of which they are conscious 

 — meaning by tone, I assume, shade of colour, irrespec- 

 tive of what that colour may be — so that all colours of 

 similar shade look alike to him — say a neutral grey as to 

 a totally colour-blind man. It is an attractive theory in 

 that it might account for cases of trout seeing likenesses 

 between the artificial fly and the natural fly where man sees 

 only differences — such as the case of the Blue or Grey Quill 

 being taken for the pale watery dun at least as well as, 

 if not better than, the Little Marryat, or of the Orange Quill 

 being taken for the blue-winged olive or its spinner — at 

 dusk. It does not, however, seem to account for cases 

 within one's daily experience on chalk streams where a 

 single pattern proves fatal to the trout after a whole series 

 of other patterns of apparently similar shade have been 

 ostentatiously ignored. It is suggested by some that 

 trout looking up at the fly from below always see it more 

 or less black against a background of sky. There may be 

 instances where this is approximately true, but they must 

 be comparatively few, and more frequent at night than 

 by day, and in either case only when the fly is between the 

 fish and the source of light. Where the source of light is 

 behind the fish^or at either side he will, I am convinced, 

 see (or at any rate be in a position to see) far more colour 

 than the theory under consideration would permit one to 

 suppose. The position is, of course, quite different where 



