1068 REPORT— 1898. 



Experiments made with Tradescantia, Symphoricarpus, Allium, Elodea, 

 Spirogyra, agree most satisfactorily -with these theoretical results. 



Additional interest arises from the fact that these values of x really correspond 

 to optimal solutions, in which the cells live longer than in any other. 



3. On the Unit to he adopted for Osmotic Measurements. 

 By Professor Dr. L. Errera. 



The investigations alluded to in the preceding note have proved that de Vries' 

 constant isotonic coefficieyits, excellent as they are for a first approximation, are 

 not sufficiently exact for more minute experiments. Here it is advisable to use, 

 instead of them, the coefficients of electric conductivity, which vary slightly with 

 the concentration of the solution. 



Thus, osmotic pressures are not strictly proportional to the concentration of the 

 plasmolysing solutions, and these pressures ought no more to be expressed in mole- 

 cule-grams of KNO3, as is now generally done. The use of an atmosphere as 

 unit, though better, is also objectionable, as it varies from one place to another. 



I would therefore suggest to adopt the C.G.S. unit of pressure, viz. 1 dyne 

 per sq. cm., or rather (to avoid useless decimals) 1 myriadyne per sq. cm., i.e. the 

 pressure of 10,000 dynes per sq. cm., the dyne being the force which gives the mass 

 of 1 gram in 1 second an acceleration of 1 cm. per second. 



This unit is roughly equal to ^^ J^ atmosphere ; it is found to be very con- 

 venient for all sorts of osmotic calculations. 



4. The Knight-Darwin Law. By Francis Darwin, F.R.S. 



The Knight-Darwin law in its briefest form is a positive statement that no plant 

 self-fertilises itself for perpetuity. It was shown that in this I'orm it cannot be 

 found in Knight, and that Darwin adopted the more general statement that 

 Nature abhors perpetual self- fertilisation. Modern writers are inclined to condense 

 Darwin's contribution to Floral Biology to serve such aphorism, or, rather, to 

 accept .such aphorism, as a condensation of his contributions, and when exceptions 

 to it occur, or when it does not explain everything, to attempt to construct new 

 foundations for their science. It was shown that the foundations on which it rests 

 are not in need of such an underpinning process, and Darwin's generalisations still 

 suffice. The true interest of the Knight-Darwin law is in relation to wider 

 questions of sex, and not simply as a basis for the study of Horal mechanism. 



5. Striccture 0/ the Yeast-cell. By Professor Dr. L. Eerera. 



A study of the cells of Sacckaromyces Cerevisice has led me to the following 

 conclusions, part of which merely confirm former researches : 1. A relatively large 

 nuclear body exists in each adult cell. 2. Young cells contain no such body ; a 

 little later the old nuclear body divides, and one of its two daughters wanders 

 through the narrow connecting-channel into the young cell. 3. Alter the division 

 is complete, the twu cells are still kept together by a mucilaginous neck-shaped 

 pedicel, which appears not to have been noticed hitherto. It may pei'sist or not, 

 thus explaining the occurrence of cell-chains or of isolated cells in difterent races 

 of Yeast. 4. Carbohydrates are stored up in Yeast in the form of glycogen, which 

 accumulates or disappears from the vacuoles very rapidly, according to conditions 

 of nutrition and growth. The colour given by a known quantity of iodine-solution 

 to a known amount of Yeast-culture shows these variations most sharply. The 

 change of tint by heat after iodine-action, and the destruction of the intracellular 

 glycogen by saliva, also give very clear results. 



