PUCCINIA. 107 



of each of the sterigmata swells into a small irregularly 

 roundish body (the sporidium), which ultimately be- 

 comes detached. 



By the above simple method of preparation the promycelium is 

 apt to be damaged ; it is much better to remove the teleutospores 

 before germination, and to cultivate them in a hanging drop of 

 water on the slide (see Part I. page 16). At the right period of 

 the year, the germination takes place in about twenty -four hours : 

 if this succeed, the additional advantage is gained from cultivation 

 on the slide, that the observer will be able to follow the successive 

 stages of the germination in an individual specimen, by repeated 

 examination of it at short intervals of time. 



It is known that the sporidia thus produced are not capable of 

 further development on the Grass plant: this only takes place 

 when they gain access to the Barberry (any species of Berberis), or 

 other plants of allied genera, e.g., MaJwnia. In order to acquire 

 evidence on this point, cultures should be prepared as follows ; 

 students must, however, be prepared for disappointment owing 

 to various technical difficulties, which will only be duly appre- 

 ciated in practice : Keep fresh, young leaves of Berberis in moist 

 air under a bell-glass, and in "drops of water placed on the surface 

 of them immerse some teleutospores which are known to be in a 

 fit condition for germination : after an interval more than sufficient 

 for complete formation of the sporidia (and De Bary states that 

 infection may occur in twenty-four hours), strip off a small piece 

 of the epidermis, or cut tangential sections from where the drop 

 was placed : mount in water with the outer surface of the epider- 

 mis uppermost, taking care to avoid pressure by the cover-slip. 

 Examine under a high power to observe the mode of germination 

 of the sporidia, and the penetration of the germinal tube through 

 the outer wall into a cell of the epidermis, whence it proceeds 

 to the mesophyll, and, branching, spreads through considerable 

 tracts of tissue : the result of this may now be studied in the 

 mature condition on the leaf of Berberis. 



