May 20, 1898.] 



SCIENCE. 



695 



value of the species or variety, and this 

 more accurately than can be done by the 

 ordinary descriptive terms. The discrimi- 

 nation of species has hitherto been depend- 

 ent upon the experience and judgment of 

 each systematist, and consequently the 

 results have often been most conflicting 

 and confusing. By the use of a precise 

 mathematical criterion of species ' splitting ' 

 and ' lumping ' is no longer possible and 

 any hybrid or intergrade, which may have 

 been described as a species or a variety, is 

 clearly shown by its intermediate position 

 and by the absence of isolation, while a 

 sport is indicated by its relative fewness of 

 individuals and its place at the extreme of 

 variation. 



The possibilities of statistical methods in 

 the study of individual variation extends 

 far beyond the applications here proposed. 

 The gradual change of the specific type and 

 of the variability of a species, the distin- 

 guishing of stable from plastic groups, the 

 influence of environment upon specific form, 

 and many other matters of importance to 

 the philosophical naturalist and systematist, 

 are in the future to be investigated quanti- 

 tatively.* 



JULIUS SACHS {II). 

 It was at Wiirzburg that Sachs first 

 found fit opportunity to develop his talent 

 for teaching. Too often it happens in lec- 

 ture-rooms that ' man Vielesieht, die nicht da 

 sind,' but this did not apply to him. His 

 fascinating, lucid expositions stimulated 

 the students, whilst he knew well how 

 to practically illustrate his subject. He 

 worked incessantly at the materials for 

 demonstrating, drew and painted a number 



* Those -who desire further information on the 

 quantitative study of species are referred to the ex- 

 cellent paper of Dr. F. Ludwig : ' Die Pflanzlichen 

 Variationscurven und die Gauss'sche Wahrsohein- 

 liohkeitscurve,' in the Botanisches Centralblatt, 73: 

 :241, 1898. 



of diagrams, and was constantly adding to 

 his stock of dried plants, alcohol prepara- 

 tions, models and cultures. He considered 

 that all should be in due relation to the 

 subject-matter in a scientific lecture as in 

 the acting of a play. In the winter he 

 lectured on general botany (anatomy and 

 physiology), and in the summer on the 

 'Natural History of the Plant World.' 

 Besides this he often gave experimental 

 demonstrations in the summer and this 

 necessitated a great deal of work ; occa- 

 sionally he lectured on the history of bot- 

 any and on the physiological basis of mor- 

 phology. After 1874 he had a class every 

 term for microscope woi-k. 



A great number of botanists worked at 

 one time or another in his laboratory. The 

 first were Dr. Kraus and Millardet (both 

 formerly at Bonn and Freiburg). Among 

 others attracted by him to Wiirzburg were 

 Baranetzky, Brefeld, Francis Darwin, Det- 

 lefsen, Elfving, W. Gardiner, Godlewski, 

 Goebel, Hansen, Hauptfleisch, Klebs, H. 

 Miiller-Thurgau, Moll, ISToll, Pedersen, 

 Pfeffer, Prantl, Eeinke, D. H. Scott, Stahl, 

 Vines, De Vries, Marshall Ward, Weber, 

 Wortmann and Zimmermann. He insisted 

 upon his pupils being in earnest about 

 science, and he brooked no laziness. Weak 

 natures naturally felt his influence most 

 strongly, but he set a higher value on those 

 from whom he could gain something. 



With failing health he withdrew more 

 and more into himself. " I am beginning 

 to take private pupils again," he writes, 

 " but there is little pleasure in it. When 

 a professor reaches the age of sixty he 

 ought eo ipso to be pensioned off with his 

 full salary ; it might be possible to arrange 

 a university that would serve as an alms- 

 house, but I would not go into it." 



He urged his pupils to make comprehen- 

 sive studies even as he was constantly 

 striving after wide generalizations. He 

 was a master in the art. We have only to 



