cH.xxivANTS AND PLANT-STRUCTURE 385 
worthy of being read there. I will here give some 
passages from Darwin's reply, dated April i, 1869. 
" The facts which you state are extraordinary, 
and quite new to me. If you can prove that the 
effects produced by ants are really inherited, it 
would be a most remarkable fact, and would open 
up quite a new field of inquiry. You ask for my 
opinion ; if you had asked a year or two ago I 
should have said that I could not believe that the 
visits of the ants could produce an inherited effect ; 
but I have lately come to believe rather more in 
inherited mutilations. I have advanced in opposi- 
tion to such a belief, galls not being inherited. 
After reading your paper I admit, Firstly, from the 
presence of sacs in plants of so many families, and 
their absence in certain species, that they must be 
due to some extraneous cause acting in tropical 
South America. Secondly, I admit that the cause 
must be the ants, either acting mechanically or, as 
may perhaps be suspected from the order to which 
they belong, from some secretion. Thirdly, I 
admit, from the generality of the sacs in certain 
species, and from your not having observed ants in 
certain cases (though may not the ants have paid 
previous visits ?), that the sacs are probably in- 
herited. But I cannot feel satisfied on this head. 
Have any of these plants produced their sacs in 
European hot-houses ? Or have you observed the 
commencement of the sacs in young and unfolded 
leaves which could not possibly have been visited 
by the ants ? If you have any such evidence, I 
would venture strongly to advise you to prociuce 
it. . . . 
VOL. II 2 c 
