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PLANT PHYSIOLOGY AND ECOLOGY 



contraction, the closing of the perianth, and the falling of the 

 corolla are the most frequent. 



Experiment 41. Pollination. Select five flowers of diflferent types, 

 representing preferably such divergent forms as the willows, grasses, 

 legumes, roses, mints, composites, etc Determine by a series of ob- 



FiG. 34. Self-pollination in Moneses uniflora by the combined movement 

 of pedicel and stamen filaments. (After Kerner.) 



servations the kind of cross or self-pollination which each shows, the 

 agent concerned, and the exact manner in which the agent works. In 

 those that are pollinated by insects, point out the various devices for 

 attraction and transfer. 



150, The period of flowering. The time at which a plant 

 opens its flowers and matures its fruits is the result of long-con- 

 tinued endeavor on the part of the species to adjust itself to the 

 climatic factors of its habitat. Since all the factors are highly 

 variable, especially heat, which is the most important in this con- 

 nection, the time of flowering varies slightly from year to year. 

 In a very abnormal season the variation becomes pronounced. 

 Flowering occurs when the amount of growth, which is chiefly 

 determined by temperature, reaches a certain stage. The neces- 

 sary sum of temperature is reached more slowly in a cool year 



