76 NATURAL SCIENCE. Feb. 



others have proved that when bacteria are cuUivated in a certain way 

 they may lose their special fermenting powers. Hansen, however, 

 was unable to demonstrate a similar behaviour in the case of alcoholic 

 yeasts. Their cells may be temporarily much enfeebled, and 

 varieties may be produced yielding less alcohol than the primitive 

 forms, but, hitherto, it has been impossible to produce one which has 

 completely lost its power as an alcoholic ferment. 



A propos of the possibility of replacing the yeast of cultivation 

 (S. cerevisice) by some of the species occurring in nature, with a view 

 to obtaining new or better products, Hansen emphasises the fact that 

 we know nothing of the history of existing supposed variations from 

 a primitive form ; for " we have never been able to carry one single 

 Saccharomyces species back to its progenitor." The question as to 

 whether the species are mere developmental phases of various 

 common mould-fungi must still be considered an open one. Since, 

 however, we now know many moulds that develop alcoholic fermenta- 

 tion fungi, it would not be surprising if some should be found to 

 develop yeast-cells with the characteristic internal spores. 



As regards the causes of the variations, Hansen finds that there 

 are three important external factors, the nutritive substratum, 

 aeration, and temperature. As regards the two former, it is only 

 required that they should allow of a vigorous multiplication, and the 

 range in which they may vary is a wide one. But as regards 

 temperature, one or two degrees too much or too little is enough to 

 prevent the changes. If the temperature is a little too low the effect 

 will not be sufficiently marked, if too high, the multiplication of the 

 cells ceases too soon, and the change that has begun does not become 

 fixed. 



The Nutritive Materials in Wheat-grains and Wheat-embryos. 



It is a fact familiar to students of botany that the seeds of 

 flowering plants correspond, not to an eg^ that has just been fer- 

 tilised, but to an egg within which the chick-embryo has proceeded 

 some little distance in its development, and has then for a time 

 become quiescent. In some seeds, such as, for instance, the common 

 broad-bean, the young embryo has absorbed the whole of the food- 

 material which had been provided for it, and has packed that into its 

 young seed-leaves. Thus, the part of the bean or of a walnut which 

 one eats is the actual embryo. In other seeds, as for instance wheat- 

 grains, the embryo remains very small until it germinates, and the 

 part which is ground into flour and used as food is the endosperm or 

 food-store, not yet absorbed by the embryo. In the number of the 

 Annals of Botany referred to in our last paragraph, Mr. O'Brien gives 

 the results of investigations he has made into the composition of the 

 endosperm or food-store, and the germ or embryo of wheat-grains. 

 The embryo is richly stored with aleurone-grains, thus contrasting 

 with the endosperm, in which the proteid material is stored as gluten. 



