No. 463.] STUDIES ON PLANT CELL. VI. 455 



in a number of structures with their contents somewhat massed 

 at one side or in the center but such conditions must not be 

 confused with the remarkable process of synapsis Jn_the spore 

 mother-cell. Among all the excellent studies of gametogenesis 

 in the Peronosporales I cannot find any clear evidence of a re- 

 duction of the chromosomes at gametogenesis. 



Quite different is the account that Trow (104) brings forward 

 to support his view of chromosome reduction during gametogen- 

 esis in the Saprolegniales. Trow describes two mitoses in the 

 oogonium of Achlya debaryana : in the first the number of chro- 

 mosomes is eight which becomes reduced to four in the second. 

 Trow's account of a second mitosis in Achlya is very different 

 in a number of particulars from the results of all investigations 

 on gametogenesis in the Peronosporales and Saprolegniales. 

 Two centrosomes with radiations are said to appear at the poles 

 of the spindle at anaphase, structures which were not present in 

 the first mitosis. Some of these asters become the center of 

 the egg origins and are later accompanied by deeply staining 

 material constituting a body which Trow terms an ovocentrum 

 and which perhaps corresponds to a coenocentrum. Relatively 

 few of the nuclei in the oogonium are said to pass through this 

 second mitosis and some of their products, with the accom- 

 panying asters, break down. The remainder become the func- 

 tional gamete nuclei of the eggs. There are many complex 

 activities described by Trow in connection with the appearance 

 of the asters during the second mitosis and also at the side of 

 the sperm nuclei which are said to enter the oogonium, events 

 that cannot be correlated with the processes of gametogenesis 

 and fertilization as we understand them for the Peronosporales. 

 They are treated briefly in a review by myself (Bot. Gas., vol. 

 39, p. 6 1, 1905), where, however, I misunderstood a distinction 

 that Trow draws between the aster and the ovocentrum (see an 

 answer by Trow, Bot. Gaz., vol. 39, p. 300, 1905). My impres- 

 sion is that either Trow has been mistaken in his interpretations 

 or that there are present events which must entirely change our 

 conception of gametogenesis in the Saprolegniales and Perono- 

 sporales, but which are not fully explained by Trow's paper. 



Let us now think of gametogenesis among the thallophytes 



