40 
MEMOIR OP 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 1 77*’, 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 1775 the professorship of natural 
history became vacant by the death of Dr. 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, — ho 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 
