xxiii.] SUMMER RUST AND MILDEW. 157 



three stops, joints, or septa, as at B, C, D, and from each 

 of the three separate pieces three fine branches arise, and 

 these branches bear at their tops three irregular oval 

 transparent, very pale amber-coloured spores, as illustrated 

 at E, F, G. These spores are the third of the series. 

 First we have Uredo, or rust spores ; then Puccinia, or 

 black mildew spores ; last, spring or pro-mycelium spores. 



Pro-mycelium spores germinate very readily in a film 

 of water on glass, as illustrated at H, by the protrusion 

 of a fine tube of mycelium. 



In a state of nature the black Puccinia spores germi- 

 nate upon straw, as it rots on the ground in the spring, 

 and the minute ovoid pale lemon -coloured spores are 

 carried about in the air in millions that, too, in the 

 springtime, when corn first becomes invaded, and when 

 the first signs of summer rust or Uredo appear upon our 

 cereals. 



Judging by what is well known amongst other fungi, 

 it would be perhaps reasonable to suppose that these little 

 hyaline spores (particularly as they arise from specialised 

 resting-spores) would reproduce the rust from which they 

 were originally derived (and nothing else), if they came 

 in contact with grasses. Many botanists believe this to 

 be a fact ; others say they do not, but, on the contrary, 

 that the cycle of corn mildew is not complete with the 

 production of these spores. Many observers believe that 

 before the pro-mycelium spores can cause the rust of corn 

 they must be nursed by a barberry bush ; that the lemon 

 coloured spores invariably refuse to eifectually grow on 

 the leaves of grasses, but when placed on the leaves of 

 barberries they find themselves so thoroughly in a natural 

 position that they do not, on germination (like the majority 

 of fungus spores) gently follow the uneven surface of the 

 leaf cells, and so quietly enter by the stomata ; but the 

 mycelium from the spores, it is said, sinks into the hard 

 leaves of the barberry, through the cells of the epidermis 

 (not between them) to the body of the leaf, and there, 



