14 Esther Pearl Hensel 



another side to admit a cork for holding the thermometer in 

 place. Two alcohol lamps were also found necessary, one to 

 heat the box in which the platits were placed, the other to heat 

 water in a retort, and thus pass water vapor into the box and 

 produce a moist atmosphere. Self-registering thermometers and 

 psychrometers were of great aid in taking readings of control 

 conditions. Besides taking advantage of low temperatures in 

 the open, or in cold rooms, double- walled bell jars packed with 

 snow or ice were used to obtain low temperatures. 



In all the experiments, strong, healthy plants were used, and 

 no experiments were performed with flowers cut off from the 

 plant. Wiederscheim, in his researches of 1904 on the crocus 

 and tulip, and also Pfeffer and Jost, have affirmed that they have 

 obtained the same results with flowers cut off from the plant as 

 with those on the plant. Wiederscheim has even performed ex- 

 periments successfully with all but one perianth leaf removed. 

 However, unless this fact is thoroughly proved as in the instance 

 just mentioned, it is much safer to work with the plant intact. 



Unless otherwise stated, all observations apply to flowers in 

 the greenhouse. 



EXPERIMENTS 



The plants directly experimented with were the common dan- 

 delion (Taraxacum taraxacum), the cultivated four o'clock 

 [Mirabilis jalapa), the cultivated morning glory {Ipomoea pur- 

 purea), the evening star {Mcntselia nuda), the large evening 

 primrose (Pachylophus caespitosus) , and the common flax 

 (Linum usitatissimum) . Four of these are ephemeral types, one 

 hemeranthous (the dandelion), and one nyctanthous (the eve- 

 ning r.tar). 



Hemeranthous and nyctanthous ^flowers open and close be- 

 cause of temperature variations, and temperature variations 

 alone. They undergo a resting period, they sleep, while ephem- 

 eral flowers in closing end their existence, and therefore tem- 

 perature variations only prolong or hasten this process with 

 them. Hemeranthous and nyctanthous types can be made ephem- 

 eral, or at least shorter lived, by the addition of more heat than 



204' 



