Morphologie, Befruchtung, Teratologie, Cytologie. 567 



den, was Verf. auf die Wirkung eines chromatinlösenden Enzyms 

 zurückführt. Am stärksten wurden die Meta-, Ana- und Telophasen 

 angegriffen, sehr langsam der ruhende Kern, Die Spindelfasern 

 verschwinden, Kernmembran und Nukleolus bleiben im ruhenden 

 Kern erhalten, die Chromosomen werden zunächst vakuolisiert, bei 

 längerer Dauer des Versuches ganz gelöst. Zusatz von Kochsalz oder 

 Salpeter fördert die Wirkung des Enzyms, andere Salze, wie z, B. 

 Kupfersulfat, wirken hemmend. Auch die Temperatur ist von Ein- 

 fiuss: 30—40° wirken fördernd, 80 — 90° vollständig hemmend. Freie 

 Säuren verhindern die Tätigkeit des Enzyms, schwache Basen da- 

 gegen nicht. Phosphorwolframsäure ergab in den vegetativen 

 Mitosen eine Fällung, andere Fällungsmittel dagegen nicht, was auf 

 eine Spaltung der Nukleine hindeutet. Toluolhaltige Extrakte aus 

 jungen frischen Pflanzenteilen wirkten auf mit Alcohol fixiertes Ma- 

 terial ebenfalls chromatinlösend. Verf. hält es für wahrscheinlich, 

 dass das Enzym auch in der lebenden Pflanze wirksam ist. Zum 

 Schluss seiner Arbeit wendet sich Verf. gegen die Anschauung, dass 

 das Chromatin allein der Träger der erblichen Eigenschaften ist. 



Pedro Arens. 



Peapson, H. H. M., Some Observations on Welwitschia mirabi- 

 lis Hook. (Phil. Trans. Roy. Soc. London, Series B. Vol. 198. 1906. 

 p. 265 — 304. 5 Plates and 2 figures in the text.) 



The autor gives at the end of his interesting paper a very good 

 summary. A copy of this will procure us the best idea of the contents. 



The igermination of the seed of Welwitschia in Damaraland 

 apparently occurs rarely, probably only in exceptionally wet seasons. 



The maximum age attained by individual plants is probably 

 much greater than a Century. 



Plants growing in contact very readily form natural grafts, into 

 the composition of which several individuals may enter. 



Welwitschia is dioecious, and normally flowers every year. At 

 Haikamchab the sexes seem to be about equally represented. 



Pollination appears to be partly, if not entirely, due to insects, 

 as Strasburger ^states, when the ovule is well advanced, after the 

 appearance of the micropylar tube above the bract. 



There are many indications that spore-development, reproduction . 

 and the maturation of the seed proceed with unusual rapidity. 



Three hypodermal archesporia develop in each anther. The 

 course of their development corresponds very closely with the stages 

 described for Ephedra and Gnetum. 



The primary hypodermal wall-layer divides to form inner and 

 middle wall-layers, neither of which divides further by periclinal 

 walls, both are tapetal. 



The outer sporogenous cells break down and form a large Pro- 

 portion of the tapetum. 



The wall of the adult anther, a Single layer of cells, closely 

 resembles that of Ephedra in its structure and manner of dehiscence. 



The division of the spore-mother-cell is of the "simultaneous" type. 



Three nuclei are present in the poUen-grain before the anther 

 dehisces; they lie in a plane which is more or less transverse to 

 the axis of the grain. The parietal (probably prothallia) nucleus dis- 

 appears, usually before the pollen is shed. 



St'rasburger's Statement, that the middle (probably generative) 

 nucleus is situated in a distinct cell, is confirmed. There is no trace 

 of cell-walls is the pollen-grain. 



