On the Movements of Petals 25 



before, and also a little before their closing, in order to determine 

 whether the water-content of the sail had anything to do with 

 the phenomenon. No differences in per cents were obtained that 

 could be construed as influencing movement by increasing the 

 turgescence of the cells. The per cents varied very little, from 

 4-5 per cent being the normal in July and August for root depth. 



R.ather crude experiments were also carried on to measure the 

 amount of transpiration in shoots bearing flowers about to open, 

 and also those about to close. Vigorous blooming shoots were 

 cut off and placed in large test tubes well stoppered, the shoot 

 fitting into the stopper through a split in the latter, the end rest- 

 ing for an inch or more in the water. The amount of water 

 transpired was practically the same during the day and night, 

 showing that turgescence is not the efficient stimulus. 



I also tried shading the plants continuously to induce an earlier 

 opening, but it was not possible to get a sufficient change in tem- 

 perature by this means. 



Relative humidities taken just at the top of the plant at the 

 time of opening vary extremely, as also those taken at the time 

 of closing. When the flowers were opening, relative humidity 

 values from 17. i per cent to 95.6 per cent were obtained between 

 2:45 ^i^*^ 6:45 P.M.; when the flowers were closing in the morn- 

 ing, between 6:00 and 7:00 a.m., values from 54.2 per cent to 

 63.8 per cent were obtained. It is evident, then, that the water- 

 content of the air does not influence opening, as neither do water- 

 content of the soil nor light. That temperature is the controlling 

 factor can only be deduced from temperature readings taken at 

 the times of opening and closing, for, as mentioned earlier in 

 the paper, it was impossible to grow Mentzelia in the greenhouse, 

 and in the field conditions were extremely hard to control. As 

 to figures showing temperatures at which the flowers open in the 

 afternoon from 2:45 ^ 7:45 p.m., the range is from 14%° to 23° 

 C, while the corresponding range of temperatures when they 

 close in the morning is from 8° to 16.8° C. 



215 



