

398 MB. F. DARWIN ON THE GLANDULAR BODIES ON 



Sporidia scarcely perfect, but apparently much smaller than in C. teru- 

 ginosum. The matrix is not discoloured. 



435. Cenangium brasiliense, Mont. Ann. des Set. Nat. s£r. 4, v. 



371. 

 On bark, Goyaz (Wedd.). 



436. Phacidium dentatum, Kunze,Berk. in Hook. Journ. (1851) 17- 

 Caripi (Spruce). 



437. Rhizomorpha corynephora, Kunzein Weig. Exs.; Berk, in 



Hook. Journ. (1856) 277- 

 S. Antonio de bon vista, Rio Javary (Tr a ill, no. 173). Panure ( Spruce, 

 no. 149). Traill's no. 22 is also a Rhizomorpha. 



On the Glandular Bodies on Acacia sphcerocepJiala and Cecropia 

 peltata serving as food for Ants. With an Appendix # on the 

 Nectar-glands of the common Brake Fern, Pteris Aquilina* 



Bv Francis Darwin. M.B.. F.L.S. 



[Itead June 1, 187G.] 

 (Plate VI.) 



■ 



These structures were discovered by Mr. Belt ; and the part 

 which they play in the economy of the plant is described in his 

 delightful book*, from which the following description is taken. 



Fig. 1 (Pl.V I.) represents a small branch of Acacia sphcerocephala ; 

 at the base of the petiole is seen a pair of sharp curved spines, h h, 

 from which the tree receives its name of the BulPs-horn Thorn. 

 These spines are hollow and are inhabited by ants ; and at 

 certain seasons hundreds of the colonists may be seen running 

 about over the young leaves, passing in and out of their nest 

 through an aperture made at the base of the spine. The ants 

 form a standing army for the tree, and not only prevent cattle 

 &c. browsing on it, but also protect it from the ravages of the 

 leaf-cutting ants. So serious is the latter danger, that the tree is 

 actually unable to exist without its guard of colonists. To ensure 

 the presence of ants about the young leaves two attractions are 

 offered by the Acacia : — first the nectar secreted by a crater-formed 

 gland situated at the base of the petiole, and shown at g g in fig. 1 ; 



* ' The Naturalist in Nicaragua/ 1874, p. 218. 



