PREFACE 
Notwithstanding the considerable number of books 
dealing with mycology that have appeared in this country 
during recent years, curiously enough not one of that 
number has contained a reference to those groups of fungi 
dealt with in the present volume. The reason is perhaps 
not far to seek. All the species dealt with come under 
the category of “ microscopic fungi,” and as such, are 
ignored by those mycologists who consider that fungi are 
only to be met with during the months of September and 
October. On the other hand, to those who can advance 
a step beyond the mere learning of names, and the com¬ 
pilation of lists of doubtful value, the study of microscopic 
fungi affords an insight to the origin and nature of fungi, 
which cannot be derived from a study of the higher forms 
alone. 
The mildews—Peronosporaceae, illustrate the transition 
from primitive aquatic fungi to aerial forms, also the origin 
and development of parasitism. The rusts—Uredinaceae, 
illustrate that remarkable phenomenon known as hetero- 
^ ecism, which implies that a given fungus lives on two different 
^ host-plants during different periods of its life-cycle, the 
— phase on each host-plant respectively starting from a spore 
or reproductive body. The great charm in connexion with 
the study of these lower forms lies in the fact that by means 
of infection experiments and pure cultures, much insight 
can be gained bearing on the life-history of these minute 
organisms. All the species are parasites, and unfortunately 
in too many instances prove destructive to cultivated 
plants ; hence from this standpoint a thorough knowledge 
of their nature is imperative. 
As additions to the Fungus-flora of this country are 
constantly being recorded, more especially amongst the 
microscopic forms, it has been considered advisable to 
include those species not yet met with in Britain, but which 
are parasitic on host-plants indigenous to this country; 
also those parasitic on cultivated plants. 
GEO. MASSEE. 
Kew. IVY MASSEE. 
2561 ()8 
