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Botany. — "Contribution to the knowledge of the cytological develop- 

 ment of Oenot/iera Lamarckiana", by Mr. J. M. Geerts. 

 (Communicated by Prof. F. A. V. C. Went). 



(Communicated in the meeting of September 26, 1908). 



Among the numerous plants, of which the cytological development 

 has not yet been investigated, Oenothera Lamarckiana was the one 

 selected, because a cytological examination of this plant would probably 

 he of importance for the solution of other and more general questions. 



Thus it may afterwards perhaps be possible, through aknowledge 

 of the cytology of Oenothera Lamarckiana and its mutants, to find 

 an explanation of mutation. 



Although the mutation-theory has gained acceptance in most 

 countries, this lias not hitherto heen the case in England to any 

 considerable extent. There, Bateson and his pupils regard Oen. Lam. 

 as a hybrid and attribute the origin of new species to hybrid segre- 

 gation. The cheef argument in favour of this view is that Oen. Lam., 

 like many hybrids, shows a large degree of sterility in the ovules 

 and pollen grains. 



In this investigation I therefore set out to trace when and how 

 this sterility arises, in order to be able to judge of the value of 

 Bateson's argument. 



It is quite conceivable that some day we may obtain a full 

 insight into the conditions, through which mutations arise, and also 

 that we may be able to bring about these conditions at will. For 

 this purpose experiments with Oen. Lam. are especially desirable, 

 in which attempts should be made to influence the origin of the 

 mutants by subjecting tin» flowers lo various conditions, for instance 

 of temperature, or to various conditions of humidity, to injections etc. 



In order to obtain reliable results in such experiments, it is neces- 

 sary to know exactly, not only which flowers have been subjected 

 to the influence, but also, in which developmental stage the flowers 

 were at the time of treatment, whether before the synapsis, before 

 or after the reducing division etc.: for then only can we determine 

 whether a change in the number of mutants is really the result of 

 the treatment, or is produced by other, unknown causes. 



In order to make this investigation available fur such experimental 

 investigations, I have therefore also followed oul the developmcnl of 

 the flower, so as to be able to icier the principal cytological con. 

 ditions to externally visible stages. 



With reference to the mutants and hybrids of Oen. Lam. many 



18 



Proceedings R«ya) Acad. Amsterdam. Vol. XI. 



