THE EVENING-PRIMROSE FAMILY. 201 



IV. Using still older specimens, observe and describe 

 the structure of the fruit and its mode of dehiscence. 



Physiological Adaptations. 



If possible, visit both in the daytime and evening the 

 place where the plant is growing, and study its habits. 

 Ascertain when the flower opens, whether its color and 

 odor are attractive to any particular class of insects, and 

 whether the length of the calyx-tube or any other struc- 

 tural features indicate special adaptations. Endeavor to 

 ascertain by direct observation how pollination is effected. 

 Accounts of this, so far, are very meager, but suggest a 

 curious keeping in tow of two or more different sorts of 

 visitors, some of them coming by day and others by night. 1 



RELATIONSHIP. 



I. Obtain specimens of the great willow-herb, or fire- 

 weed, Epilobium angustifolium, L., often very abundant on 

 newly cleared land that has been burnt over, and compare 

 the plant throughout with what you have seen of the 

 evening primrose. Note 



1. Habits and external characters. 



2. Structure of the flower, especially its plan and the 



relation of the various whorls to each other. 



3. Adaptations to insect visitors. Observe particularly 



the position of the style in flowers of different 

 ages, and the time when the stigmas open. Is this 

 before or after the anthers have shed their pollen ? 



NOTE. This species furnishes an excellent example of proterandrous 

 dichogamy.' 2 



1 Cf . Lubbock, I.e. ; Miiller, Fertilization of Flowers, p. 264. 



2 Cf. Gray, Structural Botany, p. 222. 



