406 ANEMOrHILOUS PLANTS. Chap. X. 



Francis has discovered, the large glands at the bases 

 of the fronds, but only whilst young, excrete much 

 sweetish fluid, which is eagerly sought by innumerable 

 ants, chiefly belonging to Myrmica; and these ants 

 certainly do not here serve as a protection against any 

 enemy. In S. Brazil, however, ants attracted by the 

 secretion to this plant, defend it, according to Fritz 

 Miiller,* against other leaf-devouring and highly de- 

 structive ants; so that, if this fern originated in tropical 

 S. America, the capacity of secretion may have been 

 acquired for this special purpose. Delpino argues 

 that sugar-secreting glands ought never to be con- 

 sidered as merely excretory, because if they were so, 

 they would be present in every species ; but I cannot 

 see much force in this argument, as the leaves of some 

 plants excrete sugar only during certain states of the 

 weather. That in some cases the secretion serves to 

 attract insects as defenders of the plant, and may have 

 been developed to a high degree for this special 

 purpose, I have not the least doubt, from the observa- 

 tions of Delpino, and more especially from those of 

 Mr. Belt on Acacia sphserocephala, and on passion- 

 flowers. This acacia likewise produces, as an additional 

 attraction to ants, small bodies containing much oil 

 and protoplasm, and analogous bodies are developed 

 by a Cecropia for the same purpose, as described by 

 Fritz Miiller.t 



The excretion of a sweet fluid by glands seated 



* See a lettec in ' Nature,' June Acacia. With respect to the Ce- 



1877, p. 100, by my son Francis, cropia, see 'Nature,' 1876, p. 304. 



with interesting extracts from a My son Francis has described the 



letter by Fritz Miiller. microscopical structure and deve- 



f Mr. Belt has given a most lopment of these wonderful food- 

 interesting account (' The Natu- bodies in a paper read before the 

 ralist in Nicaragua,' 1874, p. 218) Linnean Society. Bot. vol. xv. 

 of the paramount importance of p. 398. 

 ants as defenders of the above 



