136 DIMORPHISM IN FUNGI. 



ground in the spring. The pro-myceUum, as it is called, gives rise 

 to the pro-mycelium spores, which are carried about the air in 

 millions. We have thus again the three processes: — the Uredo, or 

 rust-spores ; the Fuccinia, or black mildew spores ; and the spring, 

 or pro-mycelium spores. Some botanists hold that the process is 

 now completed, and that the pro-mycelium spores just reproduce 

 the Uredo spore again. Others hold that the cycle of the corn- 

 mildew is not complete with the production of these spores, but 

 that these spores jDass on to another host — the barberry — and 

 there produce an recidial form, which in turn gives rise to the 

 Uredo spore. 



We now, therefore, pass from the first to the second division 

 of our subject, where the various forms appear on a wholly dis- 

 tinct and different matrix ; in fact, heteroecism, pure and simple. 

 Heteroecism is accepted as a fact by, I believe, all continental 

 botanists, and by many also in this country. It is still, however, 

 rejected as unproven in this case by such mycologists as Dr. M. 

 C. Cooke and Mr. Worthington Smith. As Mr. Plowright is the 

 chief investigator on the subject in this country, I shall quote his 

 observations first. Living in a district where the wheat-mildew 

 was very fatal to the crops, and where the theory of the barberry 

 blight being connected with it was very prevalent amongst agricul- 

 turists, he determined to investigate the matter by experiment — 

 viz., by infecting a number of wheat-plants with ripe spores of the 

 barberry fungus. The result was that while 76 per cent, of the 

 infected plants took the disease, no less than 70 per cent, of 

 similar wheat-plants, kept as check plants, became spontaneously 

 affected with mildew. In consequence, he wrote in Grevillea, 

 December, 1881, that he telt bound to differ from the eminent 

 botanists abroad, who accepted the heteroecism of F. graminis as 

 an established fact. In the spring of 1882 he commenced a fresh 

 series of experiments with a great deal more care than he had 

 used the first time, but having, as he says, a mind biassed against 

 the theory of heteroecism. This time, not only was barberry 

 fungus sown upon wheat under circumstances which should, as far 

 as possible, preclude the agency of accidental infection, but, con- 

 versely, the wheat-mildew was sown uijon barberry plants. All the 

 wheat plants were kept continuously covered by bell-glasses from 



