On the Movements of Petals 33 



EPHEMERAL TYPES 



Night bloomers 



Experiments with Pachylophus caespitosus. Field conditions, 

 rather than controlled experiments, were made use of here to 

 obtain information as to sleep movements, since it was impossible 

 to grow the plants in the greenhouse. The plant as observed 

 grev,' on the gravel slides of the mountains around Halfway, 

 Colorado. Its delicate fragrant white flowers open from 4:50 

 P.M. to 8:00 P.M., and close from 10:00 to ii :oo the next morn- 

 ing, when they become a dull pink color. It often happens that 

 the flower stays open the entire day when it is cool and cloudy, 

 and, rarely, on to the next day. The early or late opening in the 

 evening is not due so much to the immediate temperatures as to 

 those that have prevailed during the day, thus enabling growth 

 to go on faster and opening to occur sooner. This is shown by 

 the varied temperatures at which opening and closing occur. On 

 certain days, the flowers are still open in the morning when the 

 temperature rises as high as 31°, while in other cases they are 

 closed when the temperature is as low as 13.5° C. or as high as 

 23.5° C. Opening in the evening occurs when the temperature 

 is as high as 19.5° C. while, when it remains as low as 16.5° C, 

 they may still remain unopened. 



Plants copiously watered showed no earlier opening than those 

 normally treated. 



Experiments zvith Mirahilis jalapa. In the greenhouse, in 

 March and April, these flowers stay open until noon or after, 

 sometimes 2 :oo or 3 :oo o'clock, but occasionally are closed or 

 almost closed by 10:30 a.m. when the day has been warm and 

 bright. The opening almost never occurs at 4:00 o'clock, as 

 tradition goes, but at 6 :oo or 9 :oo o'clock or later. It is possible 

 to prolong the period of opening by lowering the temperature 

 below the normal. This is illustrated by the following tables : 



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