TAXONOMIC VALUE OF MORPHOLOGICAL CHARACTERS 29 



described Pseudococcus obscurus, stated that ". . . it did seem very im- 

 probable that the same species found on the roots of Opuntia at Los 

 Angeles, could be synonymous with a species found working on the new 

 bark of Sambucus glauca (Elder) at Santa Paula, 60 miles away." On 

 this basis it would seem even more improbable that the species found on 

 Opuntia at Los Angeles should be the same as a species found feeding 

 on the bark of wild cherry in New York. Yet the evidence now avail- 

 able indicates that both the species on Opuntia and the species on Sam- 

 bucus are identical with one found in New York on wild cherry. 



The apparent anomalies which we encounter if host and biological 

 differences be disregarded will usually disappear as our knowledge in- 

 creases and at the worst are as nothing in comparison with the anomalies 

 which appear if the morphological evidence be disregarded in the same 

 manner. It is certainly possible, if not even probable, that there exist 

 forms behaving for all practical purposes as distinct species, yet which 

 are not separable by any morphological characters that we are able to 

 appreciate. Indeed, it may eventually be worth while to designate some 

 of these forms by names, but it seems hardly desirable to take such a step 

 until all other possibilities have been exhausted. 



For the purposes of the present paper all evidence other than that 

 of morphology has been strictly disregarded. This action has been taken 

 not from a belief that biological evidence is always entirely valueless, 

 but from a conviction that it is extremely dangerous when not fully un- 

 derstood. It is too often merely misleading. 



