The Cereal Rusts. 
I. The Development of their Uredo mycelia. 
BY 
I. B. POLE EVANS, B.A. (Cantab.), B.Sc. (Wales). 
Mycologist , Transvaal Department of Agriculture, Pretoria . 
With Plates XL-XLIII. 
Introduction. 
I N recent years very considerable attention has been attracted to a group 
of species of Puccinia. the more important members of which are 
parasites of our chief cereals. All these species were at one time included 
under the three names P. graminis , Pers., P. rubigo-vera , DC., and 
P. coronata , Corda. 
Recently they have been subdivided into thirteen species, each of 
which is readily recognized by well-defined morphological and physiological 
characters. These have further been subdivided into no less than twenty- 
four forms, distinguishable from each other by apparently physiological 
characters, that of adaptation to particular hosts. 
Further, the well-known Swedish mycologist Eriksson in endeavouring 
to account for special cases of infection was led to formulate a view since 
known as the ‘ Mycoplasm ’ hypothesis, according to which the mycelium 
perennates in the form of a naked intercellular plasma. 
Unfortunately our knowledge of the cytology of these fungi, notwith- 
standing the interesting work which had been done by De Bary (4), 
Poirault and Raciborski, Sapin-Trouffy (31), Marshall Ward (33) and 
Blackman (6), is still in a very unsatisfactory condition. 
It was obviously desirable that someone should undertake the detailed 
investigation of the histology of these forms. 
It w£s under such circumstances that the late Professor Marshall Ward 
very kindly suggested that I should attack, partly in conjunction with 
himself, but mainly working alone under his advice, some of these problems. 
The work was begun in November, 1903, and was carried on for two 
years in the Cambridge Botany School, and has since been continued in my 
own Laboratory at Pretoria. 
As would be expected, a vast amount of information relating to the 
[Annals of Botany, Vol. XXI. No. LXXXIV. October, 1907.] 
K k 
