KONINKLIJKE AKADEMIE VAN WETENSCHAPPEN 
TE AMSTERDAM. 
PROCEEDINGS OF THE MEETING 
of Thursday December 24, 1908. 
DCC 
(Translated from: Verslag van de gewone vergadering der Wis- en Natuurkundige 
Afdeeling van Donderdag 24 December 1908, Dl XVII). 
EE EE NT TE S. 
W. Borek: “On the biological significance of the secretion of nectar in the flower”, p. 445, 
W. Kapreyn: “On a theorem of PAINLEvú”’, p. 459. 
P. ZEEMAN: “The law of shift of the central component of a triplet in a magnetic field”, p. 473 
J. D. van per Waars: “Contribution to the theory of binary mixtures”. XII, (Continued), p. 477. 
A.J P. van DEN BROEK: “About the development of the urogenital canal (urethra) in man”. 
(Communicated by Prof. L. Bork), p. 494. (With one plate). 
Jan DE Vries: “On bicuspidal curves of order four”, p. 499. 
E. H. BücnNer and Miss B. J. KarsreN: “On thesystem hydrogen bromide and bromine”. 
(Communicated by Prof. A. F. HorreMan), p. 504, 
Miss T. Tammes: “Dipsacan and Dipsacotin, a new chromogen and a new colouring- 
matter of Dipsaceae”. (Communicated by Prof. J. W. Morr), p. 509. 
A. F. HorLEMAN and J. J. Porak: 1. “On the bromation of toluol” 2. “On the sulfo- 
nisation of benzol sulfonic acid”, p. 511. 
Botany. — “On the biological significance of the secretion of nectar 
in the flower.’ By Dr. W. Burck. 
(Communicated in the meeting of November 28, 1908.) 
In an article in the Recneil des travaux botaniques Néerlandais 
vol. IV.*) I have explained in detail, that Darwin in 1859 put 
forward the hypothesis, that a cross with another individual is 
indispensable for (he species and that, at the time, he considered the 
structure of flowers to be generally such as to ensure, or at least 
to favour, eross-fertilisation, but that in later years he, however, left 
this stand-point. I showed from his later writings, that the observa- 
tions and experiments of many years had brought him more and 
more to the conclusion, that a much greater significance should be 
attached to self-fertilisation, than he had at first imagined; I also 
showed that, at the close of his studies, he was not very far from 
giving a negative answer to the question whether floral structure 
favours cross-fertilisation. Since then, observations have been made 
on a number of tropical plants, the flowers of which are always 
closed, so that in such plants the possibility of cross-fertilisation is 
1) An abstract of this may be found in Biolog. Centralblatt. Bd. XXVIII. 
N°. 6. 1908. 
30 
Proceedings Royal Acad. Amsterdam. Vol, »i. 
