ECOLOGY 271 



and serve as a ground cover. Such accumulations retard evaporation from 

 the soil, prevent rapid changes in soil temperatures, and exert other useful 

 functions. They furnish shelter and food for many animals and fungi. As 

 they decay, they produce heat which may be taken advantage of by many 

 animals. For example, the brush turkeys in Australia depend largely on 

 the decay of plant remains for the incubation of their eggs. These birds 

 scratch together great piles of leaves and twigs and place their eggs within. 

 They watch their rubbish heaps jealously and on warm, sunny days re- 

 move some of the material above their eggs, but during cold, wet weather 

 they pile on more. Certain centipedes, salamanders, lizards, and insects take 

 advantage of the heat generated by the decay of fallen logs to keep their 

 eggs and young warm. 



The vegetation cover over a tract of country also conserves and holds 

 water in a more general way. The accumulation of living and dead roots, 

 stems and leaves, serves as a great sponge which retains water after rains. 

 In various countries where forests and other vegetation have been thought- 

 lessly removed, disastrous floods have followed. Of course floods do not 

 always result from denudation, but the removal of vegetation is perhaps the 

 most important factor. 



There are many remarkable relations between flowers and animals. 

 Flowers offer various "inducements" to attract visitors. Bright colors and 

 characteristic odors make them easy to find; "rewards" to visitors take the 

 form of nectar, pollen, and other foods. In return for such "favors" animals 

 carry pollen from one flower to another and cross fertilization between 

 different plants is thus insured. Some flowers show a high degree of adapta- 

 tion for particular visitors. They furnish convenient landing stages, post 

 color signals which indicate the shortest routes to the gifts of food, and 

 have complicated entrances which prevent the stealing of "offerings" by 

 unwelcome visitors. Some flowers depend largely on small birds for pol- 

 hnation and show corresponding adaptations. They are usually red in color 

 and have long trumpet-shaped corollas. Other flowers possess special 

 features which fit them for "fertilization" by bees, wasps, flies, butterflies, 

 moths, beetles, or other animals. Avocado trees have two different types 

 of blossoms on a single tree. The male flowers on a particular tree may 

 open only in the morning, but on a nearby tree they open in the afternoon. 

 On the same trees the female flowers will be open on the first in the after- 

 noon and on the second in the morning. Insect visitors are thus pretty 

 certain to carry pollen from one tree to another, and not between flowers 

 on the same tree. The blooming of many flowers occurs at a particular time 

 of day, and the insects which best carry their pollen are active at such hours 

 but quiet at others. Flowers are often protected from creeping marauders, 

 such as ants, by having separate "offerings" of honey exposed below the 

 flowers; by isolation in or above water; by sticky secretions; by slippery, 

 smooth or waxy surfaces; and by other means. 



