2 Esther Pearl Hensel 



some genera, as in Mentzelia, the sepals may stay reflexed after 

 the first opening. 



For convenience, flowers which are influenced in their open- 

 ing and closing by the amount of heat present may be grouped 

 into four classes as follows : 



I. Day-bloomers. 



1. Those that open only during the day, but for two or 



more (sometimes several) days in succession (hemer- 

 anthous). 



2. Those that open only during one day or part of a 



day, then the corolla withering, deliquescing, or drop- 

 ping at once (ephemeral-hemeranthous). 



II. Night-bloomers. 



3. Those that open only during the night, but for suc- 



cessive nights (nyctanthous). 



4. Those that open for only one night or part of one night 



(ephemeral-nyctanthous) . 



All flowers not included in these types open at any time of the 

 day or night and stay in this condition through day and night 

 until the end of their existence, irrespective of the amount of 

 heat present. Whether a flower is a day-bloomer or a night- 

 bloomer seems to depend upon nothing so much as habit, the 

 conditions surrounding the plant, its environment, in no way in- 

 fluencing this aspect. The purpose of this paper is to explain 

 the causes of opening and closing in any type by means of 

 experiments. 



The form of the corolla and its physical condition when ma- 

 ture, i. e., dry shriveling, deliquescing, deciduous when yet fresh, 

 etc., do not seem to influence the kind of movement ; any type, 

 for instance day-bloomers, may have the extreme variety of 

 forms of corolla, from undi\nded, as in the morning glory, to 

 divided, as in the tulip ; the corolla itself may vary in its phys- 

 ical characteristics, e. g., in ephemeral day-bloomers from dry 

 shriveling in the spring lily (Erythronium albidnm) to deliques- 

 cing in the spiderwort (Tradescantia hractcata) and deciduous 



192 



