ZOOLOGY AT.JD BOTANY, MICROSCOPY, ETC. 85 



Parmelia.* — G. Bitter enters, in great detail, into the characters 

 which distinguish the species of the suhgenus Hypogyinnia of this genus 

 of Lichens from one another. The specific characters especially relied 

 on are those connected with the place and mode of formation of the 

 soredes. Nineteen species in all are described, six of them new. 



Buchner's Yeast Extract.f — The extract as obtained by A. Wrub- 

 lewski is a somewhat viscous liquid, of aromatic odour and sweet taste, 

 and exhibits a brownisb-yellow or greyish-blue fluorescence. It is 

 either optically inactive or feebly dextro-rotatory. Filtration through 

 a Berkefeld or sandstone filter diminishes, and through a Chamberland 

 filter entirely removes the fermenting power. The extract does not act 

 on starch-granules, but ferments starch-paste, soluble starch, glycogen, 

 and sucrose. In fermentation by yeast-cells, the zymase remains in the 

 cells and does not diffuse into the sugar solution. If the cells are col- 

 lected on a sandstone filter, fermentation in the sugar solution ceases. 

 The sugar solution probably passes into the cells and is there fermented. 

 Alcohol and carbon dioxide accordingly are true excreta of the yeast- 

 cells. The author believes that the zymase is not an enzyme but a 

 colloidal substance, which exists in the extract in a state of semi-solution 

 and belongs to the group of protoplasmic ferments. 



Microscopical Appearances of Pressed Yeast after Liquefaction. $ 

 — A. Harden and S. Bowland, after narrating the changes culminating 

 in the liquefaction of yeast, describe the following series of structural 

 changes which were observed microscopically. The freshly pressed 

 yeast consists of large cells with a small vacuole and granular proto- 

 plasm, staining a deep brown with iodine. As the evolution of carbon 

 dioxide proceeds, the vacuole increases in size, the brown stain obtained 

 with iodine diminishes, and just before liquefaction there is usually no 

 glycogen left in the cell. After liquefaction, the cells have no vacuole 

 and are shrunken, the cell-walls being crumpled, and the cell substance 

 highly granulated and contracted to a centrally aggregated mass, float- 

 ing in a small amount of clear fluid. No brown reaction is, as a rule, 

 obtainable, and although in the case of yeast liquefied at 50°, the brown 

 stain is obtained, the cell does not in other respects differ from the 

 normal character. It therefore seems probable that the liquefaction of 

 the yeast is due to the discharge of the contents of the vacuole, and 

 that the progressive increase in the sizo of the vacuole results from the 

 accumulation of some substance produced along with carbon dioxide 

 from the glycogen. The changes described terminating in the extrusion 

 of the contents of the vacuole were watched on the hot stage, and the 

 cell-wall could be readily distinguished throughout the process. 



Storing up of Water in the Spores of the Uredineae.§ — According 

 to P. Dietel, the thickenings which are so frequently found in the walls 

 and in the stalks of spores of Uredineae serve as a reservoir of water, 

 to prevent the spores getting prematurely dried up and thus inhibiting 



* Hedwigia, xl. (1901) pp. 171-274 (2 pis. and 21 figs.). 



t Journ. Pr. Chem., lxiv. (1901) ii. pp. 1-70. See Journ. Chem. Soc, Ixxx. 

 (1901) Abst. ii. pp. 616-7. t Journ. Chem. Soc , lxxix. (1901) pp. 1227-35. 



§ Naturw. Rundschau, xvi. (1901) pp. 41-1. See Hedwigia, xl. (1901) Beibl., 

 p. 74. 



