400 



K ELATION TO ENVIRONMENT. 



ulus were entire!}- remo^'ed. As we know also contact or [)res- 

 sure stimulus, or jarrin.u; produces the same result in "sensitive" 

 plants like mimosa, some species of rubus, etc. In many plants 

 there is no well-developed pulvinus, and yet the leaves show 

 similar movements in assuming the day and night positions. 

 Examples are seen in the sunflower, and in the cotyledons of 

 many plants. A little observation will enable any one interested 

 to discover some of these plants.* In these cases the night 

 position is due to epinastic growth, and while this influence is 

 not removed during the day the light stimulus overcomes it 

 and the leaf is raised to the day position. 



770. Leaves which rotate with the sun. — During the growth 

 period the leaves of the sunflower as well as the growing end 



Fig. 430- 

 Same sunflower plant photi;>graphed just at sundown. 



ot the stem respond readilv to the direct sunlight. The re- 

 sponse is so complete that during sunny days the leaves toward 

 the growing end of the stem are drawn close together in tlie 

 form of a rosette aiid the entire rosette as well as the end of the 



* Seefllings are usually vcr)- sensitive In light ami are gnod objects to 

 study. 



