432 BOTANY [CHAP. XI 



Letter 762 curvature or the amount of curvature is taken as the criterion. 

 Moreover they vary according to age, and perhaps from 

 vigour of growth, and there seems inherent variability, as 

 Strasburger (whom I quote) found with spores. If the curious 

 anomaly observed by you is due to varying sensitiveness, 

 ought not all the seedlings to bend if the flashes were at 

 longer intervals of time? According to my notion of contrast 

 between light and darkness being the stimulus, I should 

 expect that if flashes were made sufficiently slow it would be 

 a powerful stimulus, and that you would suddenly arrive 

 at a period when the result would suddenly become great. 

 On the other hand, as far as my experience goes, what one 

 expects rarely happens. 



Letter 763 To Julius Wiesner. 



Down, Oct. 4th, 1881. 



I thank you sincerely for your very kind letter, and for 

 the present of your new work. 1 My son Francis, if he had 

 been at home, would have likewise sent his thanks. I will 

 immediately begin to read your book, and when I have 

 finished it will write again. But I read german so very 

 slowly that your book will take me a considerable time, for 

 I cannot read for more than half an hour each day. I have, 

 also, been working too hard lately, and with very little success, 

 so that I am going to leave home for a time and try to forget 

 science. 



I quite expect that you will find some gross errors in my 

 work, for you are a very much more skilful and profound 

 experimentalist than I am. Although I always am endea- 

 vouring to be cautious and to mistrust myself, yet I know 

 well how apt I am to make blunders. Physiology, both 

 animal and vegetable, is so difficult a subject, that it seems 

 to me to progress chiefly by the elimination or correction of 

 ever-recurring mistakes. I hope that you will not have upset 

 my fundamental notion that various classes of movement 



1 Das Bewegungsvermogen der Pflanze, 1881. One of us has given 

 some account of Wiesner's book in the presidential address to Section D 

 of the British Association, 1891. Wiesner's divergence from Darwin's 

 views is far-reaching, and includes the main thesis of the Power oj 

 Movement. See Life and Letters, III., p. 336, for an interesting letter 

 to Wiesner. 



