870 ECOLOGY 



heat, cold, and wind.^ Since the calyx commonly is composed of green 

 and leaflike sepals, it probably plays an important part in food manufac- 

 ture, as well as in protection, and occasionally it replaces the corolla in 

 the matter of showiness. Sometimes bracts supplement or replace the 

 calyx as protective structures, as in Desmodium. In the composites 

 a calyx-like involucre is the chief protective organ (fig. 1194)- In ^^e 

 aroids the large spathe protects the entire inflorescence in flower as well 

 as in bud. Even the corolla may be a protective organ, as in the grape, 

 where it falls as soon as the bud opens, and in flowers which close at 

 night and in stormy weather. 



The duration of flowers. — From the standpoint of protection, 

 flowers may be divided into those that remain open throughout anthesis 

 and those that close once or more during that period. Of those which 

 remain open, many are ephemeral, and hence need but little protection, 

 particularly as opening usually comes only in favorable {i.e. warm and 

 sunny) weather. Among the latter are the flower-of-an-hour {Hibiscus 

 Trionum), which has the most ephemeral of flowers, rarely lasting for 

 more than three hours, the day lily {Hemerocallis fidva), and the night- 

 blooming cereus. In striking contrast with these are certain orchid 

 flowers which may remain open for fifty to eighty days if unpollinated 

 (as in Odontoglossum)? On the whole, plants with ephemeral flowers 

 are more likely to have a large number of blossoms in a season than are 

 plants with long-lived flowers. 



The protection of non-closing flowers. — Long-lived, non-closing 

 flowers would seem to need some protection, the greatest dangers, per- 

 haps, being the waste of pollen through rain, the drying of the stigmatic 

 surface through drought, and injury from low temperature or frost. 

 Pollen is not readily wetted, which is itself a matter of considerable pro- 

 tective importance; also it will be recalled that some pollen, such as that 

 of exposed vernal flowers, is not readily injured by wetting or by low 

 temperature. Many plants have nodding flowers, notably the ericads, 

 and also Bryophyllum and Yucca (fig. 1192), and thus are well protected 

 from injury by rain. Many of the features that protect flowers from 

 crawling insects also protect them from rain; among these are contracted 

 corolla throats (as in Arctostaphylos and in various borages), and zygo- 



' An illustration of calyx protection is afforded by the peach and strawberry, in which 

 unopened buds are much less subject to injury from frost than are buds that are partly 

 or fully opened. 



' The early withering of orchid corollas may be induced not only by pollination, but 

 also by the mechanical irritation of the stigma. 



