ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 377 



carp, until only the ascogonial cell is left, still retaining its charac- 

 teristic spindle shape, and the two nuclei, which do not fuse in this 

 cell. The development of the paraphyses and of the perithecial wall 

 was also followed. The ascogonial cell was still recognizable by its 

 plasma contents. Further nuclear development was difficult to follow, 

 but Nienburg is in no doubt that conjugate division takes place. 

 Ascogenous cells were frequently found in the young perithecium con- 

 taining a pair of nuclei. As new ascogenous cells are formed, the 

 plasma contents pass over into them, and nuclei left behind gradually 

 degenerate. The final stages were not followed. A general review is 

 given by Nienburg, and a criticism of the views of other workers on the 

 cytology of the Ascomycetes. 



As regards the spermogonia of Polystigma, the " spermatia " of which 

 are now functionless, he suggests that these may be equally regarded 

 as conidia which for some reason or other have degenerated. He is 

 inclined to trace the evolution of the Ascomycetes back to the Oomy- 

 cetes, and compares MonoUepharis with Polystigma. 



Studies on Yeast.* — Horace T. Brown has carried out a series of 

 cultures to determine the relation of cell-reproduction to the supply 

 of free oxygen. The facts which have been established experimentally 

 with regard to the reproduction of yeast-cells in a nutrient liquid con- 

 taining dissolved oxygen are summarized as follows. 1. When the 

 available oxygen is limited to that initially contained in the liquid, 

 the number of yeast-cells per unit volume tends to attain a maximum 

 which is independent, or nearly so, of the number of cells of seed- 

 yeast per unit volume, but is conditioned in the first instance by the 

 initial amount of this dissolved oxygen. 2. Within certain limits of 

 oxygen supply, the maximal reproduction is strictly proportional to the 

 initial amount of the oxygen. 3. The rate of reproduction under 

 these conditions is not logarithmic, but is a linear function of the 

 time. 4. The dissolved oxygen does not remain as such in the liquid 

 during the reproductive period, but is rapidly absorbed by the seed- 

 yeast before cell-budding commences. The author also discusses the 

 metabolism of the yeast-cell, with special reference to the thermal 

 phenomena of fermentation. The paper is illustrated by numerous 

 tables and diagrams. 



Ascosporic Condition of Aschersonia. t — Hitherto this genus has 

 been placed among the SphteropsideaB, as the pycnidial condition only 

 was known. Now Roland Thaxter has discovered the ascosporic fruits 

 which place it definitely among the Hypocreacete. There are some 

 forty species of this mostly tropical genus, and though they live on 

 leaves, and are given specific names to indicate the kind of leaf they 

 affect, they are really saprophytes on the honey-dew, and are thus ento- 

 mogenous fungi. Aschersonia is often brightly coloured, and of soft 

 consistence, but it is frequently blackened by accompanying Capnodinse, 

 which also grow on insect excreta. Aschersonia turbinata, the species 



* Ann. of Bot., xxviii. (1914) pp. 197-226. 

 t Bot. Gaz., lvii. (1914) pp. 308-13 (7 figs.). 



Aug. 19th, 1914 2 c 



