DECEMBER 17, 1903] 
NATURE 
149 
of an electrophorus (Fig. 39) until the cover has been 
earthed. 
In the further editions which will certainly be called 
for we should like to see a proof of the equation 
R~=qro, although Dr. Glazebrook (p. 63) considers the 
proof to be beyond the limits of the book. It is so 
easily done for a sphere, and the case of a plane is 
obtained at once by expanding the sphere of infinity. 
It will also be an advantage if graphical represent- 
ations of the forces of charges and currents are given. 
The concluding chapters deal with technical appli- 
cations (there is no mention of electric lighting), with 
electric waves, and with the electronic theory of dis- 
charge. 
The volume is very well printed, and is remarkably 
free from printer’s errors. But in one particular we 
must speak with great emphasis—the punctuation re- 
quires most thorough revision. Many sentences are 
unintelligible on first reading, although the wording 
is quite correct. We give the shortest illustration of 
this fault. The time ‘‘ will also depend on the re- 
storing couple being less when this is big, than when 
it is small.”’ 
PROF. JOHANNSEN ON HEREDITY. 
Ueber Erblichkeit in Populationen und in reinen 
Linien. Lin Beitrag zur Beleuchtung schwebender 
Selektionsfragen. By W. Johannsen. Pp. 68. 
(Jena: G, Fischer, 1903.) 
ROF. JOHANNSEN has set himself a hard task, 
namely, the reconciliation of the views of Prof. 
de Vries on mutations with those of the biometric 
school, particularly with the Galtonian theory of re- 
gression. We say a hard task, because to perform the 
task of reconciliation requires, on the one hand, an 
intimate knowledge of the mathematical theory of 
statistics, and on the other a power of clearly defining 
the exact biological points which are at issue. It is 
not an easy matter to distinguish between a so-called 
mutation and an extremely improbable variation; in- 
deed, the utmost caution is needed when we remember 
that in every case of continuous variation it has been 
shown theoretically that the extreme variations in popu- 
lations of even many thousands must be separated by 
wide intervals, the wider the more extreme the vari- 
ations.! Clearly it is practically impossible to dis- 
tinguish straight off between a ‘“‘ mutation ’’ and an 
extreme variation in the biometric sense. Both parties 
would probably agree that only observation of the 
results of propagating from the individual thus classi- 
fied could serve as a criterion between the two views. 
According to the biometricians, the type of the vari- 
ation would regress in the offspring, either to the 
population mean if a ‘‘ pure line’ did not exist, or 
to the “type of the pure line”’ if such did exist; in 
the latter case a change in type from that of the ‘‘ pure 
line’ could then be produced by selective breeding 
within the line for a generation or two. According to 
de Vries, no further change could take place until a 
new ‘‘ mutation’? appears. Unfortunately, de Vries’s 
Own experiments are very far from conclusive in this 
1 Francis Galton’s Difference Problem (Biometrika, vol. i. p. 390). 
NO. 1783, VOL. 69] 
respect. Thus in his experiments on clover he was not 
content with the discovery of a mutation, but went on 
stringently selecting year after year, in exactly the 
manner in which the biometrician would suggest that 
a “stock *? should be formed from extreme variations. 
According to the biometrician, two or three generations 
of selection will form a stock which, while very vari- 
able about its type, will yet breed true, or with but 
small regression. 
Prof. Johannsen seems to assume that this result 
of biometric theory (1898) is the view only of de Vries, 
who published his conception of the line ‘‘ as perfectly 
constant and yet highly variable’ three years later. 
Thus the criterion between the ‘‘ Biometriker,’’ as 
Johannsen calls them, and the ‘‘ Mutators,’? as we 
may perhaps call their opponents, cannot be made 
to turn on the breeding true of ‘‘ pure lines ’”’ or on 
the variability of such lines about their type. It 
can only turn on whether, within the ‘‘ pure line,’’ 
there exists regression and progression when we breed 
from variants which are not so extreme as to be at 
once classed by the ‘‘ Mutators’’ as new mutations. 
Prof. Johannsen had a good opportunity for dealing 
with this problem in his experimental observations on 
the bean Phaseolus vulgaris, but he has unfortunately 
not provided the exact data on which it could be 
answered. He has shown that the population of bean 
seeds, as distinguished from bean plants, exhibits 
Galtonian regression; he may, more doubtfully, be 
held to have shown that ‘‘ pure lines’ breed true. 
But this is no reconciliation of the biometric and muta- 
tional theories, for both parties accept the breeding 
true of pure lines. 
Unfortunately Prof. Johannsen seems to think that 
a single bean seed may be taken as typical of a plant, 
and thus the whole inner meaning of allowance for 
homotyposis escapes him. If his view—that pure lines 
show no internal regression—were correct, then the 
correlation between mother and daughter plants ought 
to be perfect, for either of them represents the ‘‘ pure 
line,’ and that is “‘ vollig konstant.’’ Unfortunately 
Prof. Johannsen has not determined this correlation, 
but from his published material it can be indirectly 
worked out for the case of the mean weight of the 
beans produced by nineteen mother plants and their 
daughter plants. The correlation thus obtained is 
0-59+0-13; this might be equal to the imperfect corre- 
lation of the biometricians, who find the value for man, 
horse and dog to be o.5, but it is very far from the 
perfect correlation needed by those who assert that 
there is no regression within the pure line to its own 
type. Prof. Johannsen’s own investigation of this 
problem (pp. 36-37) is quite fallacious; and this is 
owing, we think, to inexperience in the use of statis- 
tical methods. From this standpoint we should like 
to protest against any such crude process of deter- 
mining goodness of fit as that of placing a normal 
curve down on seven or eight blocks forming a ‘‘ histo- 
gram,’’ and judging the look of the fit. No such test 
is valid, and, further, he has not yet shown that the 
normal curve of errors itself is suited to describe the 
phenomena referred to. 
We hope Prof. Johannsen will continue his experi- 
