RELATIONS OF ANTS TO I'ASCULAR PLANTS. 



tains that A. fistulosa, which furnishes a gum of commercial value, is 

 never eaten by cattle and he attributes this immunity to the protecting 

 ants. Concerning the growth of the thorns he says: " Of the manner 

 in which the young inflations arise I am unable to form any satisfactory 

 conception. They are produced in great num- 

 bers at the beginning of the rainy season, when 

 the vegetation awakens, and are then green and 

 soft. I never saw a hole in one of them. Tlicy 

 arc completely closed on all sides, and it is not 

 till later that they are opened by the ants. I 

 have seen no injuries, wounds, nor anything that 

 could indicate that the deformation is due to 

 insects, and I cannot therefore regard the infla- 

 tions of the thorns as gall-formations. \Yith 

 this conclusion also harmonizes the fact com- 

 municated to me by Schweinfurth, that acacias 

 grown from seed in Cairo also developed the 

 inflations. The only explanation I can suggest is 

 that in this plant an originally abnormal growth 

 has become perfectly normal, under the influence 

 of natural selection, through adaptation to sym- 

 biosis with ants." Keller calls attention to the FlG - l8 - Broken 



. twig of sunflower (He- 



Singular fact that only a small number of the i ianfhlis annulls ) show- 

 thorns on a plant become inflated. This sug- 

 gests that bacteria or other pathogenic organisms 

 may be responsible for the deformation, which 

 is then put to good use by the ants. 



A few words may be added on certain South American plants of 

 the genera Cordia, Humboldtia, Ficus (e. g., iittrqiialis), Tococa (Figs. 

 170 and i/i) and Triplaris (Figs. 166, B and 167) and the East 

 Indian Clcrodendron fistulosum. All of these have preformed cavi- 

 ties either in the stems or in bursse on the leaves and petioles. 

 Clerodendron is said to have in the internodes preformed thin spots, 

 or prostomata, which are selected as entrances by the ants (Colo- 

 bopsis clcrodendri). The leaves of this plant are furnished with 

 innumerable nectaries along the midrib on the lower surface. In 

 Cordia nodosa the flower-bearing stem is dilated above and contains a 

 short, conical cavity which, according to Schimper, is not homologous 

 with the medullary cavity of other plants, as its walls are formed by a 

 fusion of a number of stems. The chamber, which is furnished with a 

 small preformed opening above, is commonly tenanted by ants. Schu- 

 mann (1888) and Metz (1890) have noted the remarkable fact that 



ing ants (Myrmica 

 brcrinodis) caught and 

 killed by the exuding 

 sap. (Original.) 



