PLANT COMPETITION 165 



nectary are of decisive influence. Floral competition is at work in 

 many communities throughout the season, but it is probably most in 

 evidence in meadow and prairie in early summer, when it may have a 

 critical effect upon fertilization and seed production. Some species 

 avoid competition to a certain extent by blooming earlier or later, 

 but the number of pollinators is likely to be less at such times also. 

 More effective evasion is secured by species that flower at unusual 

 times or for brief periods, as with nocturnal and many ephemeral 

 blossoms. A decisive advantage may also be obtained by such speciali- 

 zation as will favor a particularly skillful pollinator, such as red 

 flowers which have long tubes especially adapted to hummingbirds. 



Competition between Plants and Animals. From what has been 

 said previously, it is manifest that plants and animals will compete 

 with one another only when they need the same thing. As a result, 

 such a coaction is hardly to be expected of green terrestrial plants, 

 but may occur with parasites and saprophytes, aquatic forms, and in 

 small degree with soil organisms. Such competition is primarily for 

 food, but it may concern materials, like lime and silica, or working 

 conditions, as oxygen. Dependent plants must secure their food sup- 

 ply from green plants directly or indirectly, much after the fashion 

 of animals, and hence the two will come into competition with one 

 another when they are living on the same host, even though not side 

 by side. This is likewise true of saprobes, for example, bacteria and 

 Infusoria, whether in water or soil, and it obtains in some measure 

 in respect to geophilous fungi and the soil fauna. In both soil and 

 water, there is inevitable competition for oxygen whenever the air 

 content runs low, and a similar result ensues when great numbers of 

 diatoms and radiolarians make excessive demands on the supply of 

 silica, or coralline algae and anthozoans upon calcium carbonate. 



There are occasional instances of direct competition between plant 

 and animal, such as is exemplified by the flower-spider, Misumena 

 vatia Clerck, which deprives the flower of pollinators. Equally strik- 

 ing, though less evident, is the competition between bladderworts 

 (Utricularia) and young fishes, a relation that Forbes (1883, a, c) 

 has emphasized as tending to decrease the number of fish. Ten 

 bladders from a plant bearing several hundred contained 93 animals 

 representing 28 species ; of the total, 76 belonged to the Entomostraca 

 and 8 were insect larvae. In ponds or lakes with well-defined com- 

 munities of this plant, it is evident that its competition might prove 

 decisive, at least in local areas. 



