DIMORPHISM IN FUNGI. 135 



they do not germinate till the following spring, when they burst 

 amongst old decaying grass or straw, and both segments will pro- 

 bably throw out transparent threads of mycelium (sometimes 

 called pro-mycelium). As these pro-mycelial threads increase in 

 length, the protoplasm pours from the spore into the tubes, and a 

 series of septa appear, enclosing the protoplasm in the growing 

 end of the tube. From this end two or three minute, transparent 

 yellow spores arise, termed pro-mycelium spores, which speedily 

 fall from their slender supports and germinate readily on damp 

 surfaces. 



Summer Rust and Mildew. 



This is still more destructive than the spring species, farmers 

 sometimes losing 75 per cent, of their whole crop from its ravages. 

 This Rust is called Uredo linearis, and makes its appearance in 

 June and July. It is of a darker orange colour than the Spring 

 Rust, and is larger and more robust in growth, and thus splits and 

 lacerates the cuticle of the affected plant more completely, other- 

 wise the general description is the same. A section through one 

 of the pustules, magnified 200 diameters, shows the great differ- 

 ence in the size of the pustules, and also that the Ui'edo spores 

 themselves, besides differing in colour, differ also in shape from 

 the Spring Rust. They resemble it, however, in the ease with 

 which they are detached from their stems. The germinating 

 process is much the same as in the Spring Uredo. The germ tube 

 follows the minute depressions formed where the constituent cells 

 of the epidermis meet, and by following these it ultimately arrives 

 at one of the stomata, which it enters, and branches right and left, 

 ramifying among the green constituent cells of the leaf. Fresh 

 crops of Uredo spores are everywhere produced till the whole 

 plant is permeated by the mycelium. As the summer advances, 

 the rust mycelium gradually ceases to produce rust spores, and 

 instead produces the blackish-brown Piiccinia, or resting spores. 



Piiccinia grajiiinis. — The pustules of F. graminis are much 

 larger than those of P. riihigo-vera. A section magnified 200 

 diameters shows a difference in the shape of the spores, which are 

 mounted on larger stems, in the absence of paraphyses. These 

 spores follow precisely the same course as those of P. nibigo-vcra. 

 They may be found germinating upon straw as it rots on the 



