Botany. — “A method of recording growth under various external 
influences”. By V. J. Koninespercur. (Communicated by Prof. 
rr Ae Pe ©. WENT). 
(Communicated at the meeting of November 26, 1921). 
Introduction. Since the researches of Braauw *) the problem of the 
influence of “stimulus” on growth has called the attention of the 
investigators. Hitherto BLaauw’s experiments have only been affirmed 
and extended by others on the base of the “‘photo-growth-reactions”’. 
BrLAAUW’s own method was always used i.e. determining growth by 
means of a horizontal microscope in weak red light, other external 
conditions being kept as constant as possible. That even this method 
is not quite perfect has been shown lately by Miss Cr. Zo.Likorrr ’), 
who found that weak red light too exerts its influence upon growth. 
Moreover the method of microscopical measurement would fail 
entirely for research concerning the influence of gravity upon growth 
as, e.g., with this method, accurate definition of growth on a clinostat 
is impossible. 
Preliminary experiments, done with the same apparatus with 
which Miss Zorrikorer has worked (magnifying power 90 >) made 
it clear, that even errors, due to physical causes (vibrations, etc.) 
are not excluded. Since irregular values in measuring growth of an 
Avena-coleoptile were obtained, the latter was replaced by a 
micrometer-slide. Having focussed the microscope at a fixed line on 
this micrometer, the position of this line was determined every 
three minutes. Instead of an unvariable position, the following 
variations were found during half an hour: 
+12; +8; —15; +0; +3; —10; +7; +15; —12;4-7u. 
A small horizontal adjustment of the microscope, necessary at 
this enlargement at the slightest nutation of the seedling, led to 
errors varying from + 52 to — 68 u. 
The impossibility of measuring growth on a clinostat and in full 
darkness with this set of apparatus is clear. Moreover the larger 
1) A. H. BLAAUW. Zeitschr. f. Bot. 1914, 6., id. 1915, 7., Meded. v. d. Landb. 
Hoogeschool, Wageningen, 1918, 15. 
3) CLARA ZOLLIKOFER. Proc. Kon. Akad. v. Wet. Amst. Vol. XXIII. 1920, NO. 4, 
