xvi STOEY OF BUST IN WHEAT 197 



wheat alone ; much had to be learnt about fungi 

 in general, before this particular fungus could be 

 understood. 



We find, therefore, that the next stage in the 

 study of rust was one which did not seem to have 

 anything at all to do with that particular disease. 

 About the middle of the nineteenth century a 

 French botanist called Tulasne began to study 

 fungi carefully, and he soon discovered a curious 

 fact. This was that quite a number of fungi occur 

 in different forms and on different plants. 



Let us think what this means. A primrose 

 growing in a wood and a primrose in a garden are 

 both primroses, even if the garden one is larger 

 or finer, or in some way slightly different from the 

 wild one. But there are many fungi which can 

 grow in different situations, or on different plants, 

 and then they are so different in appearance that 

 no one would believe, without proof, that they had 

 any connection with one another. Tulasne showed 

 that there were a great number of cases of this 

 kind. Now it is very easy to show that the fungus 

 on the barberry is very different from the rust of 

 wheat, but Tulasne's work showed that this differ- 

 ence did not make it impossible that the two were 

 nearly related. 



The next step was actually to follow the history 

 of the rust throughout the year, to see exactly 



