ON Drosera rotundifolia 5 



leaves and destroy the plant by eating the terminal bud. Many 

 of the fragments of partially eaten leaves fall onto the Sphagnum 

 and produce new plants by regeneration. Here again is an 

 arrangement which may be considered a reciprocal adaptation; 

 the larvae are protected from the leaves which could consume 

 them, and the destruction of the plant by the larvae results in 

 vegetative reproduction. As the larvae grow older they increase 

 greatly in size and become green. Even after they have reached 

 a size which renders their capture by a Drosera leaf impossible, 

 they continue to crawl along the under surface and eat the leaves 

 from behind. They become exceedingly voracious and a single 

 insect can devour a dozen flourishing plants in two days. 



6. Cultivation 

 The Drosera plants used for experimentation were grown in 

 uncovered dishes exposed for at least six hours a day to direct 

 sunlight. Small flies and other insects were placed on the leaves 

 from time to time. The best leaves were selected for reactions 

 and were not fed. In one remarkable instance, a house-fly was 

 placed on a small fresh leaf which was only slightly pigmented. 

 A copious secretion resulted which enveloped and digested the fly. 

 After five days, however, the entire leaf-blade had disappeared, 

 being digested by its own fluid. The plant was not vigorous and 

 the fly was too large for the leaf, but normally anti-enzymes or 

 other adequate means must be present to prevent autolysis. 



7. Mechanics of Movement 

 (a) Normal Development 

 The blade of the undeveloped Drosera leaf is rolled up. As it 

 expands the marginal tentacles are seen to be bent over the blade, 

 the glands pointing against the leaf and the pedicels arranged like 

 rays around the edge. As the leaf grows, these tentacles increase 

 considerably in length, the growth being greater on the adaxial 

 side. By this means the incurved tentacles are straightened, a 

 process which is assisted by the simultaneous flattening of the 

 leaf-blade. When all the tentacles are straight, the leaf is mature 

 and able to catch insects. The full grown tentacles do not increase 

 perceptibly in length. They remain in this condition for about 



