On the Movements of Petals 15 



is normal. This is shown by the difference in the actual life of 

 a flower blooming in the spring or in midsummer: the common 

 dandelion lasts three to five days in the spring, while in mid- 

 summer two days is normal, on account of the more intense life 

 of the flower at that time. On the other hand, ephemeral flow- 

 ers can be made longer lived by the opposite process, the life 

 processes going on less intensely than normal, as numerous ex- 

 periments with the morning glory have shown. 



The dandelion, four o'clock, morning glory, and flax were ex- 

 perimented with in the greenhouse, the plants being grown from 

 seed, and the evening star and evening primrose in the open, 

 since it was impossible to grow them in the greenhouse either 

 from seeds or by transplanting the young seedlings. The diffi- 

 culty probably lay in the fact that the change of climate, altitude, 

 etc., was too great, from 9,000 ft. above the sea at Halfway, 

 Colorado, to 1,200 ft. at Lincoln. At any rate, it was impossible 

 to grow them at all from seeds, even when these were seasoned. 

 The young seedlings of Mentzelia, transplanted in the fall from 

 the mountains in Colorado to the university greenhouse at Lin- 

 coln, grew for a short time, but soon died, while those of the 

 evening primrose grew fairly well during the whole year but 

 showed no tendency to flower. 



The experiments which follow seem to me to prove quite con- 

 clusively that variations in the amount of heat present are the 

 causes of opening and closing movements among hemeranthous 

 and nyctanthous types which are not ephemeral, and also second- 

 arily in the latter. It is the sudden variations within a few 

 hours which cause flower movement. Seasonal variation in tem- 

 perature effects opening and closing scarcely at all, even in types 

 of flowers (ainthous) which bloom throughout an entire season 

 or more as the dandelion. In May it opens between 7 :oo and 

 8 too o'clock in the morning, in July between 5 :oo and 7 :oo, in 

 August between 7 :oo and 8 :oo, and in September between 7 :oo 

 and 9 too. The plant accommodates itself gradually to these 

 changes, and opening and closing occur regularly with, perhaps, 

 onlv a few hours difference in time. 



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