262 STRUCTURAL BOTANY 



We are now acquainted with the full normal life- 

 history of Puccinia graminis, which affords a typical 

 instance of the phenomenon known as heterascism, this 

 term implying that the parasite at different stages of its 

 career necessarily inhabits two distinct hosts. In this 

 case we have seen that on the Wheat or other members 

 of the Grass Family, two forms of fruit the uredospores 

 and the teleutospores are produced. The latter on 

 germination give rise to sporidia which infect the other 

 host, namely, the Barberry. It is only on the Barberry 

 that the ^Ecidium fructification and the spermogonia are 

 developed. The aecidiospores once more infect the Wheat 

 or some allied plant, and the cycle is complete. 



The fact that the Barberry has something to do with 

 the appearance of rust in Wheat was well known to 

 practical farmers, long before botanists found out the 

 scientific explanation, or even allowed the truth of the 

 observation. During the last century a vast amount 

 of evidence was accumulated showing that Barberry 

 bushes acted as centres of infection, from which rust 

 spread over the cornfields. So strong was this convic- 

 tion among agriculturalists, that in the year 1755 a 

 " Barberry Law " was enacted in the province of 

 Massachusetts in North America, ordering the rigorous 

 extirpation of Barberry bushes throughout the province. 

 The preamble to the Act runs thus : " Whereas it has 

 been found by experience that the Blasting of Wheat 

 and other English Grain is often occasioned by Barberry 

 Bushes, to the great loss and damage of the inhabitants 

 of this province ..." etc. The true explanation " that 

 the parasitic Fungus of the Barberry and that of Wheat 

 are one and the same species," was first suggested 

 by Sir Joseph Banks in 1805, and fully confirmed a 



