40 GENERAL BOTANY 



manner of adjustment varies in different plants, but all plants 

 secure a fair adaptation to the environment in which they live. 

 The dandelion. In the dandelion (Taraxacum officinale) 

 (Fig. 24) the root system resembles that of the clover plant in 

 the form of the main taproot and in the pro tropic and diatropic 

 responses of the main and lateral roots to gravity. The leaves 

 are diaphototropic and are arranged in the form of a rosette, 

 with the smaller leaves in the center alternating with the larger, 

 outside leaves. 



The scapes, or supporting stalks, of the flower clusters of 

 the dandelion, however, manifest a great variety of responses to 



gravity, and these movements 

 are evidently closely corre- 

 lated with the various stages 

 in the development of the 

 flowers and the fruit. They 

 thus furnish an interesting 

 example of the fact, often ob- 

 FIG. 23. Corresponding positions as- served in plant movements, 

 sumed by the leaflets of red clover during t ^ at t ^ e na t ur e of the response 

 the day and at night ,, 



or a given organ to an out- 



a. position of the leaflets in normal daylight; -j a . i 



6, positions of the same leaflets at night. Slde influence, or stimulus, IS 



Note that the position in 6 is assumed by apparently determined, at any 



curvature of the pulvini , . , f 



given time, by the stage of 



development and the internal condition of the organ or part. The 

 dandelion scapes are sensitive to light, but the movements here 

 figured and discussed are, for the most part, controlled by gravity, 

 and hence the light stimulation is not taken, in to account. 



In Fig. 24 the various stages in the development of a single 

 flower cluster and its fruit are shown, beginning with the bud 

 stage (a) and ending with the final seed-shedding stage (A). 

 By placing the plant upon a slowly rotating disk connected 

 with a clinostat it can be determined that the various positions 

 assumed by the scapes in the figure are a result of the response 

 of these scapes to gravity. The scapes are therefore either 

 apogeotropic or diageotropic at different stages of development. 

 In the early bud stage (a) the scape is short and the bud is 



