640 BACTERIAL DISEASES OF PLANTS 



ON INTERPRETATION OF PHENOMENA 



First of all, you are to remember that very often things 

 are not what they seem ! Two sets of phenomena may resemble 

 each other superficially but be of quite unlike origin. Herein 

 lies many a pitfall for the unwary. Probably most blunders 

 in science result from failure to distinguish between similarity 

 and identity, between resemblances that are fundamental and 

 must depend on community of origin, and those that are only 

 superficial and consequently must have diverse origins. The 

 student, and the older worker as well, should be on his guard 

 continuously against the fallacy of mistaken identity. The 

 difference between a careful worker and one who is sometimes 

 careless, or habitually so, lies in just this, that the latter sees the 

 superficial similarity and is content with an inference, while the 

 former probes the inference, demonstrates its non-validity, and 

 saves his reputation. 



Laziness, or inhibitions due to overwork, lie at the bottom 

 of most such blunders, I think, but sometimes over-confidence. 

 Usually it is quite easy to show that a given result corresponds 

 exactly to another or differs from it in various particulars, if 

 environmental conditions are duplicated, and if cultures are 

 made and sections are cut and studied, but all this takes time and 

 painstaking care, which some persons are loth to give. It also 

 involves good judgment and good training. Especially must 

 you demonstrate, if you have made inoculations and obtained 

 results: (1) that the resulting lesions are identical with those 

 occurring naturally on the plant; and (2) that the organism 

 in the lesions is identical with the one isolated from the natural 

 disease and used for the inoculations. Not to do these two 

 things thoroughly well is to leave your whole paper a tissue of 

 uncertainties. 



" Verify everything!" is the best advice I can offer. Then 

 you w r ill have no after regrets. Nearly every productive 

 scientific man, however, has some regrets of this sort. 



ON REPETITION OF EXPERIMENTS OTHER PEOPLE'S, ONE'S OWN 



There is a mistaken notion abroad that if someone has 

 worked on a subject and published a book or paper, that settles 



