ANTS AND PLANT-STRUCTURE 407 



[When I compare these and similar instances 

 with the Pitchers of the Nepenthes, in which (as I 

 learn from the accounts of travellers) ants as well as 

 water are nearly always found, I cannot doubt that 

 those curious appendages have attained their actual 

 dimensions through the deepening 'and widening 

 which they have undergone from ants through 

 untold ages.] 



We have a curious example, in the genus 

 Cinchona, of the supposed correlation of a minute 

 structural peculiarity with chemical and medical 

 properties. Eminent botanists, 'such as Weddell 

 and Karsten, who have studied that ^enus in its 



c> 



native forests, have thought they had found a char- 

 acter in the leaves always associated with a bark 

 rich in alkaloids, viz. the presence of a small pit or 

 scrobicule in the axil of each vein on the underside 

 of the leaf. But when good specimens of C. sitc- 

 cirubra, the richest of all the barks in alkaloids, 

 came to be examined, the leaves were found entirely 

 destitute of scrobicules ! See now how this comes 

 about. The leaves of the Hill Barks those, namely, 

 that grow at an elevation of 8000 feet and upwards 

 are liable to be infested by a small mite which 

 nestles in the scrobicules has caused them, in fact- 

 its remote ancestors having at first sheltered in the 

 vein-axils ; but C. succirubra grows always below 

 that elevation indeed, as low down as 2400 to 6000 

 feet and is the only quinine-producing Cinchona 

 that descends so low, the other species of Cinchona 

 that grow at a low elevation having all medically 

 worthless bark. But as all these species, C. suc- 

 cirubra included, are equally destitute of scrobiculate 

 leaves and of mites, the reasonable inference is that 



