454 THE A At ERIC AN NATURALIST. [Vou XXXIX. 



phytes in which a reduction of the chromosomes is reported just 

 previous to or during gametogenesis. The best known case is 

 Fucus since this type has been studied by three investigators : 

 Farmer and Williams ('98) and Strasburger ('97a). They agree 

 in describing the nuclear figure that differentiates the oogonium 

 from the stalk cell as exhibiting a large number of chromosomes 

 (28 or 30) while the three mitoses within the oogonium, which 

 give rise to the eight eggs, present only one half that number 

 (14 or 15). Apparently there is a reduction by one half just 

 before the mitoses in the oogonium. Since there is no sporo- 

 phyte generation in Fucus it is of course difficult to compare 

 these conditions with those in higher plants, but, as will be 

 explained later, there are some reasons why we should not 

 expect to find reduction phenomena at gametogenesis in any 

 thallophyte. 



Reduction phenomena at gametogenesis have also been sug- 

 gested for various types of the Peronosporales and Saproleg- 

 niales but not, however, in exactly the same way as in Fucus. 

 There are always, as far as is known, one or two mitoses within 

 the oogonium before the gamete nuclei are organized and it has 

 been held that these are reduction divisions by Rosenberg for the 

 Peronosporales and by Trow for the Saprolegniales. Rosenberg 

 (: O3b) described for the oogonium of Plasmopara a condition of 

 synapsis in the nuclei preceding the two mitoses and compared 

 this sequence with the events of sporogenesis in higher plants 

 in which the two divisions within the spore mother-cell are pre- 

 ceded by a period of synapsis. Rosenberg did not determine the 

 number of chromosomes in the vegetative nuclei so that he has 

 no positive evidence of reduction in the oogonia. With respect 

 to the two mitoses and the preliminary synapsis I have already 

 pointed out in criticism of Rosenberg's studies (Bot. Gaz., vol. 

 36, p. 154, 1903) that the number of mitoses is variable in the 

 oogonia of the Peronosporales and Saprolegniales and apparently 

 entirely absent in the species of Vaucheria studied by myself 

 (Davis, :O4a). Also, the phenomenon of synapsis, which is 

 easily recognized in the large nuclei of the spore mother-cell, 

 would be difficult to establish in the small nuclei within the 

 oogonia of the forms mentioned above. Nuclei can be found 



