Oil the Moz'cments of Petals 



19 



present, but never to make the flowers stay open longer than 

 usual by increasing the amount of heat to a httle more than nor- 

 mal. The point at which opening occurs seems to be from 15° 

 to 18° C, in the greenhouse, generally nearer the higher limit. 



In the experiments which follow, relative humidities will usu- 

 ally accompany the temperatures, simply as additional proof that 

 they are not influential in causing movement. For convenience, 

 different parts of the greenhouse in which experiments were 

 performed will be indicated, especially in those cases where the 

 plants are transferred from one part to another to obtain the- 

 different conditions present there, thus: south house, north house, 

 east house, middle house. The situation of plants placed out of 

 doors will be indicated as open, that of those placed in the tin box 

 with increased temperature as zvarm chamber, those placed in 

 double walled bell jars packed with snow or ice, eold ehainber, 

 those in bell jars with saturated air, moist ehamber, those in dry 

 bell jars, dry ehamber, while that of those in the compartment 

 made of black cambric will be indicated as shade tent. 



Flowers which do not open at the usual tim.? in the morning 

 because of low temperature, can be opened in from fifteen min- 

 utes to an hour by placing the plant in the warm chamber de- 

 scribed on page 13. 



On March 30, 1904. a cloudy day, dandelion flowers remained 

 closed all the morning in the greenhouse. When the temperature 

 was artificially increased in the warm chamber, in dry air or with 

 vapor, opening occurred as in the several cases cited below. 



209 



