40 MEMOIR OF DR. WALKER. 



ber of striking marks of differential similarity which 

 readily escape a common observer, one of the most 

 striking of which is the effects of habit on the exter- 

 nal characters of animals and vegetables; that is, 

 the alteration produced by climate and culture ; and 

 the examples given are the dog and the cabbage, 

 both from original stocks producing varieties so 

 essentially different, as scarcely to be recognised 

 but by tracing them back to their primitive sources. 

 The last, July 1776, on the wonderful provisions of 

 Nature for the augmentation and preservation of 

 plants, their aliment, and the soils they most affect, 

 is likewise exceedingly ingenious. 



In the year 1 775 the professorship of natural 

 history became vacant by the death of I)r. Ramsay, 

 and Dr Walker, most probably through the interest 

 of Lord Kames, Was nominated his successor. Con- 

 joined as they had been in agricultural pursuits 

 and habits of intimacy, and as his lordship enter- 

 tained a very high opinion of the talents of his 

 friend, this was just as might have been expected ; 

 only there existed what ought to have been an in- 

 superable objection, he was minister of Moffat, 

 upwards of fifty miles distant from the capital ; and 

 as it was impossible that he could fulfil the duties 

 of both situations, justice, and even a decent respect 

 for appearances, required that he should relinquish 

 the one or resign the other. This, however, he un- 

 fortunately could not resolve to do. 



At that time the ruling clergymen of the Church 

 of Scotland were actuated by a strong desire for 



