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| Held, A.J. den; Held, J.J. den; Maier, E.X.. |
| In the late summer of 1969 an investigation was made on water plants and vegetations of these in the peat holes of De Haak, part of the Nieuwkoopse Plassen (province S. Holland, the Netherlands). The pools are situated in marshwood peat and mostly have a thick layer of sapropelium. The water is about 1 m deep, is slightly oligohaline, has a medium calcium content, and is as yet hardly polluted. In the south the peat holes communicate with a ditch containing water which is comparatively rich in phosphate and nitrite. The increase in pollution and in the phosphate content to the south is demonstrated by the growing abundance of Ceratophyllum demersum and/or Vaucheria cf. dichotoma Ag., accompanied by species such as Elodea nuttallii and Lemna gibba. In the... |
| Tipo: Article / Letter to the editor |
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| Ano: 1970 |
URL: http://www.repository.naturalis.nl/record/527766 |
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| Gradstein, S.R.; Held, J.J. den; Wolff, P.. |
| Revision of the Dutch species of the Bryum crythrocarpum complex. A revision is given of the collections of the Brya erythrocarpa from Holland. Delimitating the species of this group the authors have followed the monograph of the European Brya erythrocarpa by Crundwell & Nyholm (1964). 5 species have been found in Holland up till now: Bryum micro-eryithrocarpum C. MÜLL. & KINDB., B. radiculosum Brid,. B. klinggraeffii Schimp., B. violaceum Crundw. & Nyholm and B. ruderale Crundw. & Nyholm. The latter three have not been collected until 1968, B. violaceum and B. ruderale being recorded here for the first time from our country. These two species were discovered in the Southern part of the province of Limburg, a hilly area with rich,... |
| Tipo: Article / Letter to the editor |
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| Ano: 1971 |
URL: http://www.repository.naturalis.nl/record/534893 |
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| Schuckard, R.; Mennema, J.; Held, J.J. den; Uppelschoten, H.. |
| Eichhornia crassipes (Mart.) Solms in Heemstede gevonden. Op de Floristenvergadering van 3 januari 1974 werden twee vondsten van ontsnapte aquariumplanten gemeld: Pistia stratiotes L. in de Krimpenerwaard door A. J. Quené-Boterenbrood en J. Mennema (zie ook Gorteria 7, 1974, p. 28-29) en Eichhornia crassipes bij Voorschoten door Prof. Dr. V. Westhoff. De laatste vondst intrigeerde mij in hoge mate, want als ingezetene van Voorschoten voel je je onder je duiven geschoten, wanneer je in je eigen woonplaats een leuke vondst wordt „afgesnoept”. De nadere aanduiding van de vindplaats door Prof. Westhoff „in een slootje bij de kerk” was voldoende om bij de gemeentelijke plantsoenendienst navraag te doen, maar dit leverde niets op. Daar Prof. Westhoff de... |
| Tipo: Article / Letter to the editor |
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| Ano: 1975 |
URL: http://www.repository.naturalis.nl/record/526644 |
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