12 Esther Pearl Hensel 



It is to Pfeffer more than to any one else that we owe the most 

 of our knowledge on the subject of plant movement, more in 

 respect to leaves than to flowers, however. Temperature, accord- 

 ing to his view, causes the flowers of Crocus and Tulipa to open 

 and close by certain variations. A sudden rise opens them. 

 They then turn gradually back to a lesser opening, which. posi- 

 tion is kept constantly while the temperature remains stationary. 

 When the temperature is lowered a similar reaction occurs. The 

 flowers of Crocus Inteus, C. vermis, and Tulipa gcsneriana react 

 in a few minutes, he says, to a rise of ^° C. The flowers of 

 Adonis vernalis, Ornithogaluin umhcllatum, and Colchicum au- 

 tiimnale react less strongly, while those of Ranunculus Hcaria, 

 Anemone nemorosa, and Malopc trifida respond to changes of 

 5°-io° C. Plowers of Oxalis rosea, Nymphaca alba, and 'Leon- 

 todon show only a common thermonastic movement with this 

 change (5°-io° C). 



In volume I of his Plant Physiology, Pfeffer states that os- 

 motic pressure varies with temperature according to the same 

 laws that influence gaseous pressure, and hence, by a rise in tem- 

 perature of 15° C. the pressure is only raised from 100 to 105.5. 

 Thus temperature can never exercise any niarked direct effect 

 upon turgor in plants. 



The most recent publication on this subject is by Walther 

 Wiederscheim ( 1904) . Movements of petals are said by him 

 to be caused by variations in temperature. The flowers experi- 

 mented with were Tulipa and Crocus. Burgerstein and Farmer 

 say that the movement in these flowers is a variation movement 

 that occurs, not on account of growth, but by the changing, 

 lengthening, and shortening of certain tissue complexes. Jost, 

 Schwendener, the author, and Pfeffer consider them to be growth 

 movements, the latter saying that growth produces movement by 

 a change in the force of expansion occurring "simultaneously 

 and equivalently" in the two halves, but unequally fast. The 

 other three agree in saying that growth, one phase of it, either 

 opening or closing, occurs as a result of light or temperature 

 stimulus but unequally, the second movement, the counter-reac- 

 tion, occurring from interior causes, due to the stimulating ac- 

 tion set up by increase in growth of the first side. 



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