Minnesota Plant Life. 427 



to begin the development of its flowers and fruits immediately 

 after the cold of winter is past. When the growing season is 

 short, it is particularly important for plants to ripen their fruits 

 speedily, or they will not be able to ripen them at all, and under 

 such stress, in the plants of cold countries, very rapidly growing 

 flowering stems are produced. Arising from a fleshy root, a 

 starch-packed tuber or a solid bulb, they open their first flower 

 perhaps within a week after the snow has gone, finishing their 

 fruits before the end of spring. Such unnecessary haste in a 

 climate like that of Minnesota indicates an adaptation to a 

 colder region ; and the willows and poplars, for example, which 

 scatter their fruits in the spring or early summer, may be found 

 abundantly distributed far to the northward, even to the barren 

 lands of arctic Canada. More leisurely plants which do not 

 ripen their fruits until the late autumn, such as the grapes, the 

 gourds, the goldenrods and the asters, by this very fact show 

 their southern ancestry, and they will be found better developed 

 in the south than in Minnesota. The colors of flowers, the meth- 

 ods of hibernation and the presence or absence of reserve organs, 

 such as bulbs, are all of much value in determining the probable 

 climatic history of a plant. 



Some movements in plants are significant as indicating an 

 adaptation against loss of heat. A great many flowers close 

 at night. This is particularly true of the flowers of northern 

 plants, though it is a device which is common enough in many 

 species growing in regions where the nights are cool. By 

 the closing of the flower nocturnal radiation of heat is dimin- 

 ished and thus the pollen spores are protected against unde- 

 sirable chills. Sometimes the flowers do not close, but place 

 themselves in peculiar sleep-positions. Thus a pansy flow r er, 

 which is erect in the daytime, bends over and faces the ground 

 at night. Such new night attitudes are not limited to flow- 

 ers, but may be adopted by leaves as well. At night the 

 leaves of the clovers and locust trees will be found in quite differ- 

 ent positions from those which they maintain during the day. 

 The nocturnal position is probably a device for limiting the 

 radiation from the plant body. Incidentally it is useful in pre- 

 venting the condensation of dew. Such modified positions are 

 sometimes taken suddenly, as by the leaves of the sensitive 



