Botany. — “Photo-growth reaction and disposition to light in Avena 
sata’. By H. L. van pe Sanne BAKHCIJZEN. (Communicated 
by Prof) RAR. Cs Were). 
(Communicated in the meeting of May 3, 1919.) 
Of late years our knowledge of the influence of light on the lon- 
gitudinal growth of plants has been considerably extended and 
deepened. While earlier investigations were generally content not to 
make their first observations until some hours after the beginning 
of illumination, attempts were made in more recent investigations 
to study as closely as possible from the very beginning of exposure 
the changes to which growth is subjected. 
In 1914 Braauw published his investigations on the photo-growth 
reaction in Phycomyces*), and Voer found in 1915 a similar reaction 
in the coleoptiles of Avena’); besides two further papers were 
published by Braauw on this reaction in seedlings of Helianthus *) 
and in certain roots *). 
All these investigations were carried out under the influence of 
the new points of view which Braauw and FroéscueL had opened 
up in. 1909 on the subject of phototropy; hence attention was not 
confined to the intensity, but a definite amount of light energy was 
administered. In some cases illumination was continuous ee 
the experiment. 
While Voer does not discuss the theoretical bearing of his results, 
Braauw uses his photo-growth reaction as a basis for a discussion 
of the phenomena observed in phototropy. Formerly it was indeed 
known that phototropic curvatures arise through growth being 
changed somehow by unilateral illumination, but since it was not 
known that a brief omnilateral illumination has an effect on longit- 
udinal growth, it was impossible to obtain any accurate conception 
of the changes which growth underwent immediately on unilateral 
1) A. H. Brauw. Licht und Wachstum. I. Zeitsch. f. Botanik. 1914. 
2) E. Voer. Uber den Einflusz des Lichts auf das Wachstum der Koleoptile von 
Avena sativa. Zeitschrift f. Botanik. 1915. 
3) A. H. Braauw. Licht und Wachstum. II. Zeitschr. f. Botanik. 1915. 
4) A. H. Braauw. Licht und Wachstum. III. Mededeelingen van de Landbouw- 
hoogeschool. Deel XV. 1918. 
