874 



ECOLOGY 



than the closure of perianth segments is effected by low temperature, 

 a few seconds commonly sufficing. Such closure is of direct value in 

 protecting pollen from rain. It may be recalled, also, that in anthers, 

 dehiscence generally is caused by desiccation, so that the first opening 

 is unlikely to occur in wet weather. Many plants show movements of 



the flower axes (pedi- 

 cels) or inflorescence 

 axes (peduncles). In 

 certain instances the 

 buds are erect and 

 the flowers pendent (as 

 in AquUegia). More 

 closely related to floral 

 movements are those 

 cases in which the 

 flower is erect by day 

 and pendent by night 

 and in rainy weather 

 (as in Geranium and 

 Anemone); in the um- 

 bellifers there is a simi- 

 lar movement of the 

 entire inflorescence. 

 Such movements are 

 due to growth inequali- 

 ties in the pedicels or 

 the peduncles, and the 

 advantages therefrom 

 would appear to be in 



Figs. 1195-1197. — Growth movements accompany- 

 ing flower and fruit development in a wild onion {Allium 

 cernuum): 119S, a flower bud, showing the nodding posi- 

 tion of the young peduncle (p); b, spathe; 1196, a shoot 

 in full bloom; note that the peduncle {p) has straightened 

 out except at the tip ((); the flowers are arranged in an 

 umbel, the pedicels {p') being oriented in various direc- 

 tions; note the exserted stamens (j); 1197, a shoot in 

 fruit, showing the conspicuous capsules (c) ; note that the 

 pedicels (/»') have become erect or ascending. 



exposure to pollinating 

 insects in sunshine, and in protection from rain and cold during the 

 night or in rainy weather. In the poppy the buds are nodding, but the 

 flowers are erect, the pedicels becoming apogeotropic. Movements of 

 much complexity, but without obvious advantages, are seen in Allium 

 cernuum (figs. 1195-1197), where the nodding bud becomes erect by 

 differential growth in the peduncle, while later the fruits become erect 

 by similar growth in the pedicels. 



Protection during fruit development. — Usually the developing ovules 

 are delicate. Ultimately the enveloping ovary walls and seed coats 



