COOKE, ON MICROSCOPIC FUNGI. 271 
with regard to those attacking men and animals; and it is 
now well understood that some of the most inveterate forms 
of disease amongst the mammalia are dependent on the at- 
tacks of minute fungi. So analogous are the diseases pro- 
duced in plants and animals by the attacks of fungi, that 
some speculators have not hesitated to affirm their belief in 
the fungoid nature of the poison germs which produce the 
more alarming contagious diseases that afflict mankind. It 
is only by the aid of the microscope, and the suggestions of 
such theories as the above, that we can ever expect to make 
out the nature of those poisons which, generated in one body 
aud conveyed to another, produce such terrible destruction 
of our race. Wherever the truth lies, it cannot be determined 
but by an accurate observation of facts; and as these facts 
cannot be made visible to the naked eye, to the microscope 
we must look for unfolding these great mysteries of onr lives. 
Mr. Cooke does not, however, dwell on the forms of fungi 
which attack the human body. ‘This is less to be regretted, 
as the subject, as far as it was understood, has been illus- 
trated by Robin and Kiichenmeister. The work of the last- 
named author has been translated into English and published 
by the Sydenham Society. We give another example of Mr. 
Cooke’s book im the description of a very common form of 
fungus occurring on a very common plant, and which enables 
any person with a microscope to take a peep at the field of 
research comprehended in Mr. Cooke’s volume : 
“ What is the external appearance presented by the ‘ white rust’ 
of cabbages, and allied cruciferous plants, is soon told. During sum- 
mer and autumn it occupies the surface of the leaves and stems of the 
shepherd’s purse (Capsella bursa-pastoris), with elongated narrow 
white spots like streaks of whitewash, and later in the season the 
leaves of cauliflowers and cabbages become ornamented with similar 
patches, arranged in a circular manner, forming spots as large asa 
sixpence. Wherever these spots appear, the plant is more or less de- 
formed, swollen, or blistered, even before the parasite makes its 
appearance at the surface. These white pustules have a vegetative 
system of ramifying threads which traverse the internal portion of 
the plants on which they are found; these threads constitute what is 
termed the mycelium. Not only when the plant is deformed and 
swollen with its undeveloped parasite do we meet with the threads of 
mycelium in its internal structure, but also in apparently healthy 
portions of the plant, far removed from the evidently infected spots. 
These threads are unequal in thickness, much branched, and often 
with thick gelatinous walls filled with a colourless fluid. They creep 
insidiously along the intercellular passages, and are provided with 
certain appendages in the form of straight thread-lke tubes, swollen 
at their tips into globular vesicles. These threads do not exceed in 
length the diameter of the mycelium which bears them. The 
appendages communicate in their interior with the mycelium, and 
contain within them the same fluid, which at length becomes more 
