264 
evaluation of Balmer’s constant with extraordinary 
closeness from Planck’s constant and the electron 
constants. Bohr’s work may prove very valuable 
in the solution of the central problem of the quan- 
tum; for it has the merit of carrying the principle 
of Planck, already hard to understand physically, 
logically to a very extreme point, and it is by the 
accentuation of difficulties that their solution is 
usually brought about. 
It would be impossible within the limits of this 
notice to discuss the rest of the book adequately. 
It is sufficient to say that it deals with all the 
more firmly established developments in_ this 
branch of physics, and that the names of the 
writers are a guarantee of its value. C. G. D. 
BOOKS ON PLANT DISEASES, 
(1) The British Rust Fungi. By W. B. Grove. 
Pp. xii+412. (Cambridge: University Press, 
1913.) -Piice 4s. net: 
(2) Mildews, Rusts, and Smuts. By George 
Massee, assisted by Ivy Massee. Pp. 229+ 
iv plates. (London: Dulau” and (Co¥) Lid; 
LOZ) raices7s: Od. net. 
(3) The Fungi which Cause Plant Disease. By 
Prof, F. L.. Stevens. Pp. vii-+75q. . (New 
York: The Macmillan Co.; London: Macmil- 
lansand Co., Ltd:, 191g.) . Price 37s. net. 
(1) HE twenty-four years which have elapsed 
since Dr. Plowright published his 
classic monograph of the British Uredinez and 
Ustilaginez have seen great progress in our know- 
ledge of the biology and classification of the 
former group—the rusts. Their hetercecism was 
a recognised fact; the life-history of Puccinia 
graminis was familiar to most botanical students, 
but the subject has broadened considerably in the 
last quarter of a century; P. gvaminis itself has 
been shown to include several species easily 
separable by form and colour; and, further, bio- 
logical differences have been demonstrated, em- 
bodying a close adaptation between fungus and 
host, and the recognition of “ physiological races.” 
In this connection Mr. Grove utters his protest 
against the excessive multiplication of “species ” 
by “biological” nomenclators :—‘ Physiological 
unaccompanied by morphological distinctions 
should never be allowed to constitute a difference 
of species, unless it be as a temporary measure in 
cases which have not been investigated.” The 
difficulty arising in the case of hetercecious species 
from the existence of distinct names for the 
various phases of the same species has been over- 
come by the rule agreed to at the Brussels Con- 
gress to give preference to the earliest name given 
to the perfect (in this case the teleutospore) stage. 
NOW 22324. .ViOlsIo8) 
NATURE 
| misleading. 
[May 14, 1914 
The book consists of a general and a system- 
atic part. The former comprises a useful account 
of the variously complicated life-history of the 
Uredinales, Puccinia caricis, the nettle and sedge 
rust, a species more accessible to students than 
P. graminis, the aecidum stage of which is now 
rarely found in this country, is taken as a general 
type, but full accounts of other species are also 
given. A chapter on the sexuality of the group 
supplies a review of the work done in recent 
years by Blackman and others, and its impor- 
tant bearing on the systematic relationships and 
phylogeny of the group. A chapter on special- 
isation gives some account of the “biological 
races ’’ above mentioned, and also severely criti- 
cises the mycoplasma theory of Eriksson. There 
is also a discussion of the phylogeny of the group 
and of the reasons for deriving it from the red 
algee. 
The systematic portion contains working de- 
scriptions of about 250 species, representing 
twenty-two genera and five families. The species 
in the larger genera, Uromyces (38 species) and 
Puccinia (137 species) are arranged in the order 
of the families and genera of their host-plants. 
An adequate synonymy is given, and the spores 
of a large proportion of the species are figured. 
At the end of the text are a short glossary, a 
bibliography, an index of host-plants, and a 
general index. 
(2) In the small volume, ‘“ Mildews, Rusts, and 
Smuts,’’ the author supplies in handy forrn a 
synopsis of the families Peronosporacee, Ery- 
siphacee, Uredinacee, and Ustilaginacez in so 
far as the species have been met with in Britain 
as parasites on native or cultivated plants, or are 
likely to occur, in so far as they are parasitic on 
host-plants, indigenous to this country. Some 
of the latter, by the way, have already arrived. 
The many years which Mr. Massee has devoted 
to the study of British fungi should be a guaran- 
tee of value and of accuracy, and students of our 
native fungus-flora from an economic or purely 
scientific point of view will find the book a useful 
companion. Keys are. given’ to. the) (genes 
and species, and under each species there is an 
ample description and a list of host-plants. The 
numerous species of Puccinia are arranged under 
the orders and genera of the host-plant or one 
of the host-plants, a method which is sometimes 
Thus the well-known hollyhock 
fungus, for instance, will not be found under 
Altheea, but under Malva, and in the hetercecious 
species one host only is cited, that bearing the 
teleutospores. A coloured illustration of the life- 
history of Puccinia graminis makes an attractive 
| frontispiece, and there are also four black and 
