Variation of Yeast-cells. 553 
the parent-cells from which they were descended, while in 
others no such difference could be observed. 
The above variation has thus influenced some of the most 
important morphological and physiological features, and it is 
of such a constant and radical nature that the resulting cells 
might well be regarded as constituting new species ; however, 
I described them as varieties in my earliest publications, and 
will keep this designation for the present. Although they 
have been cultivated for several years past, under most varying 
circumstances, through endless generations, still they have 
kept constant ; the newly acquired qualities have proved to be 
entirely heritable. 
II. 
The investigations mentioned above are to be found partly 
in my Recherches sur la physiologie et la morphologie des 
ferments alcooliques (Comptes-rendus des travaux du laborat. 
de Carlsberg, 1881-1891), partly in the Centralblatt fur 
Bakteriologie und Parasitenkunde, 1889, p. 638, and partly 
in the Annales de Micrographie, fevrier, 1890. A more 
detailed summary than the above may be found in my book, 
Practical Studies in Fermentation, which will appear this 
autumn, published by Messieurs Spon, London. I will there- 
fore dwell no longer on this subject, but pass on to a mention 
of my recent experiments 1 . 
About fifteen years ago I published a paper on the biology 
of Saccharomyces apiculatus , in which I pointed out, amongst 
other facts, that this yeast winters in the earth ; later, I found 
that this also holds good of the true Saccharomycetes with 
endospores. I will, in this connexion, only mention the fact 
that wine-yeasts belonging to the group S', ellipsoideus kept 
alive in the earth, like S. apiculatus , for more than three 
years. By making comparative investigations on the varieties 
1 In a fuller treatise which I am preparing at present, a detailed account of the 
phenomena of variation observed by me and of the factors and laws which 
influence them, will be found. 
Qq 
