Wageningen, centre of agricultural science in the Netherlands Authors H. de Haan DOI: https://doi.org/10.18174/njas.v5i2.17743 Downloads PDF Published 1957-05-01 Issue Vol. 5 No. 2 (1957) Section Papers License © Copyright KLV All rights reserved. The copyright covers the exclusive right to reproduce and distribute the contribution, including reprints, translations, photographic reproductions, microform, electronic form (offline, online), or any other reproductions of similar nature. The Author may publish his/her contribution on his/her personal Web page provided that he/she creates a link to http://library.wur.nl/ojs/index.php/njas and that together with this electronic version it is clearly pointed out, by prominently adding "© KLV", that the copyright for this contribution is held by KLV. The full-text version may be available from the Author's Web page only after a delay of 12 months following the publication of the paper, whereas such a delay is not required for the abstract.
