INET Ree 
601 
THURSDAY, APRIL 28, 1904. 
HETERGCIOUS RUST-FUNGI. 
Die Wirtswechselnden Rost-pilze. By H. Klebahn. 
Pp. 426 + preface, appendix, bibliography, and two 
indexes. (Berlin: Borntrager, 1904.) Price 20 
marks. 
rs 1864-65 De Bary startled the biological world with 
his discovery of the hetercecism of the Uredinea— 
with his proofs that the long suspected and often re- 
iterated connection between the peculiar yellow fungus 
known as Aicidium, growing on the barberry, and the 
well-known rust-fungus, Puccinia, which devastates 
wheat and other cereals, is true in fact, and that the 
winter-spores of the latter germinate in spring and 
develop spores which infect the young barberry leaves, 
whereon are then developed the quite different spores 
of the A®cidium, which in their turn re-infect the 
wheat. 
Investigations along the same experimental lines, 
and supported by the same irresistible logic, soon 
showed that many other Uredinez, or rust-fungi, are 
capable of a similar change of life as they pass from 
one host-plant to another, among which were the 
Gymnosporangia of junipers, which develop the very 
different Roestelia on Pomacez (hawthorns, pears, &c.), 
and the even more remarkable cases of Coleosporium 
on Senecio, which infects pines and develops thereon 
the curious ecidial forms known as pine blisters, or 
Peridermium. 
The list of hetercecious Uredinez, or rust-fungi, 
which thus change their hosts and develop a different 
kind of fungus on each host now numbers 160, in- 
cluding a few cases only where the phenomenon is not 
yet proved with absolute certainty by the experimental 
infections, and Klebahn has set himself the task of 
bringing together all the salient biological features of 
these remarkable plants, the economic importance of 
which to mankind is sufficiently indicated by the fact 
that the ravages of these parasites on our cereals and 
fodder plants, to say nothing of plants grown for 
pleasure, amount to many millions sterling every year, 
and that entire planting enterprises have been ruined 
by them. 
But the subject of hetercecism has equally important 
bearings on the scientific philosophy of plant life, 
closely bound up as it is with the large questions of 
parasitism, and the nature and origin of species. 
Klebahn’s book is divided into two parts. The first 
204 pages are concerned with the general aspects and 
discussions of the whole subject, the rest of the work 
with the special description and biology of each species 
in succession. 
A mere enumeration of the headings suffices to show 
how interesting and important are the themes discussed 
in part i. Beginning with definitions and the history. 
of the whole question of hetercecism, and a summary 
of the principal types of rust-fungi concerned, the 
author passes, in section iv., to an account of the 
means of distribution, and the conditions of germin- 
ation and infection of the various kinds of spores pro- 
duced by these remarkable fungi. 
NO. 1800, VOL. 69| 
Certain controversial questions are then examined 
and answered. Klebahn emphatically declares (p. 43) 
that no evidence of value exists to show that the host 
which bears teleutospores can be infected by sporidia. 
He also examines the question of the necessity of 
hetercecism, and concludes that for some forms it is 
indispensable, though there are many which are known 
to be able to do without it. Some of the latter have a 
perennial mycelium, the classical example being De 
Bary’s Afcidium elatinum, which induces the witches’ 
brooms on silver firs. 
By far the most exciting part of Klebahn’s general 
exposition is that which deals with the wheat-rust 
problem and Eriksson’s mycoplasma hypothesis. The 
wheat-rusts are held to be hetercecious, but able to 
dispense with the change of hosts. The wintering of 
uredo-spores is not regarded as sufficient to explain 
the infection of plants in the spring. But if the 
zecidium form is absent, and no uredo-spores have 
survived the winter, how is it the cereal shows infection 
next spring ? 
Klebahn insists on the importance of the world-wide 
distribution, in vast quantities, of the rust and of wheat 
culture, and that the wind can carry the spores, as it 
can far heavier particles such as grains of dust, 
hundreds of miles at a stretch, and Marshall Ward’s 
experiments with the uredo-spores of Puccinia dispersa 
prove that such spores may retain their germinating 
power for sixty-one days. 
Eriksson has entirely failed to grasp the significance 
of these facts, and his hypothesis of a latent and un- 
discoverable mycoplasm is not only superfluous, but 
has entirely broken down under the criticism of 
Marshall Ward’s investigations, which show that the 
so-called incipient mycelia proceeding from ‘‘ myco- 
plasm ”’ are nothing but the normal haustoria of the 
fungus. 
Section ix. deals with the distribution of rust-fungi 
and their passage into new regions. Section x. with 
methods, not only of culture and infection, but also— 
far too briefly—with the details of microscopic prepar- 
ation. Section xi. is devoted to the problems of geo- 
graphical areas of distribution, and contains much 
interesting information about the rusts of various 
countries. 
In section xii. Klebahn illustrates, with ingenious 
diagram tables, the vagaries of these parasites in their 
choice of host-plants, and then passes to the discussion 
of the second of the two great burning questions of 
the rust problem, viz. the phenomenon of specialisation 
of parasitism, with which Eriksson’s name must 
always be honourably associated. 
Put shortly, the matter stands thus. Although a 
given species of rust-fungus is found on two host- 
species A and B, and although no trace of difference 
can be discovered with the microscope in the two cases, 
nevertheless the fungus on A will not infect B, nor 
will that on B infect A. This has been so abundantly 
and thoroughly proved by the researches of Eriksson, 
Klebahn, Marshall Ward and others that there can be 
no doubt as to the facts. The explanation appears to 
be that the fungus on A is so closely adapted to the 
physiological peculiarities of its host A that it cannot 
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