370 ON THE STUDY OF MICRO-FUNGI. 



The peridia grow in very irregular patches or clusters, and 

 often cover more or less all the leaves of an infected plant. 

 Indeed, this stage of the fungus affects the host plant much more 

 prominently than do the succeeding stages, and it is consequently 

 more easily found. These cups arise from the same mycelium 

 which produced the spermogonia, and are formed at centres where 

 the mycelial tubes have become branched and gathered into small, 

 round masses. These almost spherical bodies increase in size, 

 and, when about ready to break through the cuticle, it is found 

 that in the centre of each there has been developed a number 

 of upright hyphae or branches of the mycelium, each supporting a 

 column of spores, and that this forest of hyphae and multitude of 

 spores are enclosed within a covering of barren cells. The spores 

 become filled with a yellow colouring matter, those at the tops of 

 the column coming to maturity first, but the enveloping cells — 

 though in other respects similar to the cells from which the spores 

 have been formed — remain empty. 



As soon as the aecidiospores — that is, the spores of the 

 Vadium — are ripe, the epidermis is ruptured and the fungus 

 presents itself to the world. The covering of barren cells gives 

 way and becomes curved backwards around the margin, thus 

 turning the body into a small cup, and laying bare the aecidio- 

 spores which have been produced within. PI. XVII. , Fig. 2, 

 represents a magnified section of an aecidium, and makes clear its 

 general structure. The spores at the surface of the cups being 

 ripe, and having been detached from the tube in which they were 

 developed, are at the mercy of every wind that blows, and it will 

 easily be observed how very readily they are scattered abroad. 

 On examination with the microscope, these aecidiospores will be 

 seen to be smooth and nearly spherical. In diameter they are 

 about 18 micromiUimetres (one micromillimetre= i/25,4ooths of 

 an inch). As we look into one of these cups and see the quan- 

 tity of spores which it contains, and then glance at the plant and 

 see the number of cups flourishing all over the leaves, we cannot 

 but be struck by the prodigious number of spores which there 

 must be altogether. 



Dr. M. C. Cooke, in his book^ Rust, Smut, Mildew, and Mould, 

 writes, in reference to the JE.cidiuni on the Goatsbeard, that if we 



