Stimulation and Correlation. 129 



The circumnutatory movements are due to a combination 

 of forces of which the stimulation of gravity, followed by a 

 reaction known as lateral geotropism, is the most prominent. 

 (See "Practical Text-book of Plant Physiology.") Note 

 direction of movements in a number of species that may be 

 available in a greenhouse. 



141. Carpotropic movements The movements of 



flowers by which these structures adapt themselves to changes 

 in temperature and illumination are fairly well known. 

 Familiar illustrations are to be seen in the wild carrot 

 {Dai/ctis Carota), which curves the main flower scape in such 

 manner that the flat-topped umbel of flowers which faces the 

 sky in the daytime is reversed and hung downward during 

 cool nights ; the pansy performs similar nocturnal move- 

 ments, both plants returning the flowers to an upright posi- 

 tion during the daytime. In another type of the daily move- 

 ments the flower opens or closes at certain periods of the day. 

 Thus the tulip closes on cool nights and reopens during the 

 warmer part of the day. Tussilago, Claytonia (spring beauty), 

 purslane, and many others exhibit similar adaptive reactions 

 by which the flower is protected from the effects of changes 

 in temperature and undue loss of moisture. 



In addition to such induced movements which depend upon 

 external forces for their inception, a second series is shown, 

 which are set up by internal forces, and which depend en- 

 tirely upon the developmental stage of the flower. Such 

 reactions may be classed under carpotropic movements, and 

 have for their purpose the adjustment of the flower to such 

 position as will best promote pollination and ripening and 

 dissemination of the seeds. 



Carpotropic movements are seen to be of the most di- 

 verse character. The undeveloped flower buds may be erect 

 and the ripened fruit pendent, or the reverse ; the un- 

 opened bud may be pendent, the open flower erect, and the 

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