Argues that [general variability] of species, not single variations or sports, is basis for modification and adaptation to new conditions.

DF’s opinion of Gustav Jenzsch’s book [Mikroskopische Flora und Fauna (1868)]. Encloses extract of a letter from Ferdinand Zirkel also mentioning Jenzsch’s work.

Thanks RM for his offer [see RM's 1869-1-26]; wishes astronomers would develop an accepted system of indicating the quality of observations.