264 TRANS. ST. LOUIS ACAD. SCIENCE. 



time, as in Dipsacu sylvestris, D. laciniatus, and Silphium 

 perfoliatum* 



2. By means of slippery leaves, which often have a cuived sur- 

 face, over which it is impossible for ants to climb, e.g. in Gen- 

 tiana firmd. In Cyddmen the reflexed lobes of the corolla are 

 turned upwards, so that ants cannot crawl over them. 



3. Plants, and especially parts near the corolla, are covered 

 with hairs and spines ; these often point downwards, as in flow- 

 ers of Salvia, Verbena, Linna'a, and Stachys. 



4. Some plants are especially distinguished by viscid and glu- 

 tinous secretions. These occur on the stem in Silene antirrhinu, 

 on the involucral bracts of Grindelia squarrosa, on the calyx and 

 stem of Silene noctiffora, and on the young branches of Bobinia 

 viscosa, the secreting glands shrivelling up when the flowers 

 have been pollinated. 



5. Kerner believes that the milky juices of some plants, e.g. 

 Lactnca, Asdepias, Euphorbia, Apocynvm, Chdidonium, etc., serve 

 to keep ants away. In an experiment, he found that an ant, 

 placed on a lettuce-leaf, cut the epidermal tissue with its sharp 

 claws so that the milky juice exuded, and, hardening, held the ant 

 to the leaf. 



In the cases cited, and many others of the same sort, the pro- 

 tection, though more or less effective, is usually only partial. 



To summarize: — It has been shown that flowers with deep- 

 seated nectar are often perforated, and that in most cases the 

 perforations are made by insects which are unable to get at the 

 nectar in a normal way ; that Bomhus mastriicatus is more ad- 

 dicted to this habit than any other European humble-bee, and 

 following this are Bombzis terrestris, B. pratorum, and Xylo- 

 copa violacea. Such flowers as Vicia cracca^ Aqiiilegia vulga- 

 ris^ Liiiaria vzilgaris, and others, are systematically perforated, 

 while in North America Xylocopa Virghtica is a frequent per- 



* W. J. Beal and C. E. St. John, "A Study of Silphium perfoliatum and Dipsaciis la- 

 ciniatrts in regard to Insects," Bot. Gazette, vol. xii. p. 268. F. Darwin, ''On the protrusion 

 of Protophxsmic filaments from hairs in l^ea.tC'a'p , Dipsacus aylvestris," Q^ar.]o\ir. of Mic. 

 Sci. 1877, P-2tS- F. Cohn, " Ueber vibrirendc Faden in den Driisenharen von Dipsacus," 

 Amtl. Hericht. der5o. Versammlung deutscher Naturforscher und vErtze zu Miinchen, p 

 202 (Botan. Ztg. xxxvi. p. I2j). B. D. Halsted, " Is the Cup-Plant Insectivorous?" Bull. 

 Iowa Agr. College, ;S86. p. 24. F. Ludwig, " Das Hervortreten von Protopla? mf aden bei 

 den Drusenhaaren von Silphium perfoliatum," Kosmos, Oct., iSSo, viii. p. 47. Etc. etc. 



