﻿1903] OOGENESIS IN SAPROLEGNIA 339 



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multicellular trichogynes derived from coenogametes. While 



this cannot be more than a speculation, nevertheless cytological 



and developmental investigations among the lichens and Laboul- 



beniaceae in relation to these possibilities are sure to bring forth 

 interesting results. 



We may then conceive the Ascomycetes as presenting two 

 important evolutionary lines derived from a primitive coenocytic 

 type of sexual organ (coenogamete). The first, through numeri- 

 cal reduction of potential gamete nuclei, results in uninucleate 

 sexual organs (Sphaerotheca). The second line supposes the 

 utilization of such potential gamete nuclei with cytoplasm to 

 develop such secondary sexual structures as the conjugating 

 tube of Pyronema and the trichogynes and procarpic apparatus 

 of the lichens and Laboulbeniaceae. 



It is difficult to 



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dascus to conditions in other coenogametes. Juel believes that 

 there is but one sexual nucleus in each of these multinucleate 

 gametes, the others being '* vegetative;" that there is only one 

 fusion nucleus in the fusion cell. This gives rise to a series of 

 nuclei around which the spores develop in the sac and the *'vege- 

 tative" nuclei degenerate. The details of the nuclear activities 

 are not reported, and many stages in the processes are com- 

 pletely lacking. Until we know these we must hesitate to 

 express an opinion on the position of Dipodascus. 



THE NUCLEUS OF PHYCOMYCETES IN ONTOGENY. 



A detailed and complete study of the nucleus of some Phy- 

 comycetes in the various phases of ontogeny is greatly to be 

 desired. 'At present we know a good deal about the nuclear 

 activities during gametogenesis and something at the time when 

 the oospore germinates, but the data are not complete for any 

 one form and do not explain the most important problems of 

 ontogeny. These concern the significance of the mitoses in the 

 gametangia, the relative numbers of chromosomes at different 

 periods of ontogeny, and their bearing on the sequence of gene- 

 rations, which is not well understood in this group. 



This knowledge will demand the study of one or more types 

 with attention to nuclear phenomena during vegetative periods, 



