Botany. — “On Anti-phototropic Curvatures occurring in the coleop- 
tiles of Avena”. By Dr. C. E. B. Bremexamp. (Communicated 
by Prof. G. van Irrrson Jr.). 
(Communicated at the meeting of October 29, 1921). 
In a paper published some years ago’) I discussed at some 
length the relation between the nature of the phototropic curvatures 
occurring at the tip of the Avena coleoptiles and the way in which 
those organs are illuminated. I pointed out that the origin and the 
growth of those curvatures may be interpreted satisfactorily with 
the aid of a few suppositions which present themselves rather natur- 
ally. To this end it should be assumed that the organs in question 
consist of elements furnished with a photo-sensible system, and that 
the changes which the system undergoes under the influence of 
illumination are followed after some time by changes in the rate 
of growth. The value of the latter will surely not be equal to that 
of the changes which would occur if each element could react 
independently of the adjoining ones. As a matter of fact between 
the various elements a levelling will take place’). In the second 
place it should be assumed of those elements that they are equal, 
or approximately so, and lastly that the changes in the rate of 
growth are proportionate to the changes in the photo-sensibility. 
The first-named supposition will no doubt remain hypothetical for 
the time being, since no method has been brought forward as yet 
o demonstrate the existence of those elements. However, the results 
obtained with illumination of isolated strips lend support to it. As 
to the second hypothesis it must be remarked that the elements 
alluded to are most likely not perfectly equivalent. The inner ele- 
ments are circumstanced differently from those lying immediately 
1!) C. E. B. BREMEKAMP, Theorie des Phototropismus. Rec. d. Trav. bot. Néer- 
landais. Vol. XV. 1918. 
*) It should be borne in mind, however, that owing to this levelling tensions 
must arise by which presumably the growth of the elements will be affected indi- 
rectly. In the case of the coleoptiles of Avena the value of these tensions will 
probably be insignificant, as the distribution of the light in the interior of the 
plant is, owing to the repeated reflections, rather diffuse here. It is a moot point, 
however, whether these tensions may be neglected also with organs such as the 
sporangium-bearer of Phycomyces, in which the differences of intensity in the 
interior of the plant are much larger. 
12 
Proceedings Royal Acad. Amsterdam. Vol. XXIV. 
