Nectar absondernde Driisen. 



stinging" Dalechampia ; and again those of some species of Danais on Asclepias, 

 which is protected by its milky juice." 



Down, Beckenham, May 21 1877. Francis Darwin. 



Mr. Francis Darwin has made an interesting addition to his important disco- 

 very of nectar-bearing glands on the young fronds of Pteris aquilina, supplied 

 from the ever-welcome experience of Mr. Fritz Miiller. The latter gentleman 

 finds that in Brazil the Pteris aquilina is protected from the leaf-cutting ants by 

 those attracted to the nectar, and Mr. Darwin adds some speculations on the origin 

 of the glands and their continued functional activity in Europe where they now 

 appear to be useless. On this part of the question I should like to make the 

 following remarks: 



Prof. Heer has shown that in the Miocene plant-beds at CEningen and 

 Radoboj, ants are the most numerous amongst the fossil insects, and in 1849 as 

 many as sixty-six species had been described from these two localities. In 1865 

 the number found at CEningen alone is recorded as forty-four. I do not know 

 what the total number of species is that have been recorded from the two places 

 up to the present time, but it probably does not fall short of eighty. Amongst 

 the fossil ants from Radoboj there are spezies of the Tropical American genera 

 Atta and Ponera. One of the fossil species of Atta resembles in general form 

 and in the venation of the wings the curious Atta cephalotes of Tropical America. 



As there are only about forty species of ants existing now in the whole 

 of Europe it is evident that in the Miocene epoch they must have played a 

 much more important part in Europe than they do now. Plants may then 

 have been exposed to the attacks of ennemies that have become extinct along 

 with the general impoverishment of the fauna and flora of Europe that took 

 place in Post-pliocene times; and the protection afforded by ants attracted to 

 the nectar-bearing glands at the critical stage of the unfolding of the young 

 and tender leaves may have been as important to some plants in Europe, then, 

 as it is to many in Tropical America now. 



With regard to the persistency of the nectar-producing glands up to the 

 present time in Europe, it is to be remarked that many plants are identical with 

 those living in the Miocene period and the world-wide distribution of Pteris aqui- 

 lina seems to indicate that it is of very ancient origin. If a plant has not other- 

 wise varied there is no reason apparent why it should do so in this respect so 

 long as the secretion of nectar is not positively injurious to it. I have recently 

 noticed in my garden that the ants that attend the glands at the bases of the 

 leaves of the cherry, the plum, the peach, and the apricot, stroke with their 

 antennae some of the glands that are not excreting when they arrive at them, just 

 as they do the bodies of the aphides. I have not actually noticed that this pro- 

 motes a flow of nectar, but ever since I became a disciple of Darwin I have 

 been convinced that the most trivial circumstance is worthy of notice ; and it may 

 be that the slight irritation of the glands kept up by the ants is sufficient to 

 ensure the perpetuation of a function of the plant now useless to itself. It is, 

 however, perhaps too soon to assume that the glands are entirely useless to the 



