119 



Were it not for the contrivances in many flowers, very 

 unwelcome guests would often enter the flower and utilize for 

 themselves what legitimate visitors should have. Flowers 

 are protected from unbidden guests in various ways. 



1. Aquatic plants are protected by their isolation in 

 water. Land plants have occasionally secured for themselves 

 the same advantages in that certain leaves form cups around 

 th« stem. In ottj«rs Ittere is a leaf-cup at each joint, while in 

 soHi« there is a single basin formed of the rosette of leaves at 

 the base. In these rain and dew not only collect, but are 

 retained for a considerable time, as in DipSdCiS sylvestris, 

 D- laciniatus and Silphium perfoliatum, 



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

 curved surface, over which it is impossible for ants to climb, 

 €■ g., in Gentiana firma. In Cyclamen 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 flowers of Salvia, Verbena, lAnnea and Stachys- 



4. Some plants are especially distinguished by viscid 

 and glutinous secretions. These occur on the stem in Silene 

 antirrhina, on the involucral bracts of Grindelia sqiMir- 

 rosa, on the calyx and stem of Silene noctiflora and on 

 the young branches of Robinia viscosa, the secreting glands 

 shriveling up wken the flowers are pollinated. 



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

 e. g. Laetuca, Asclepias, Euphorbia, Apocynum, Cheli- 

 donium, 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. 



