Massee : Polymorphism hi Fungi. 2.yj 



its attack. The Vaccinium has certain of its leaves more or 

 less injured, and the Ledum that becomes infected loses many 

 of its seeds without any obvious compensation. On the other 

 hand, the fungus has so arranged the sequence and period of 

 spore formation, that the spores borne on the Vaccinium host 

 are just mature when the Ledum is in bloom, whereas the pro- 

 duction of spores in the phase of the fungus parasitic on 

 Ledum, are delayed until the following spring, when young 

 Vaccinium leaves are present in abundance. When different 

 stages in the life-cycle of a fungus grow on different host- 

 plants, the term heteroecism is applied. 



Now heteroecism, the most brilliant botanical discovery of 

 the nineteenth century, made by de Bary, had its origin in 

 what was considered as a farmer's superstition. The well- 

 known rust of wheat — Puccinia graminis, had from time im- 

 memorial, been considered by farmers as in sorne way dependent 

 on a fimgus occurring on barberry bushes. De Bary, a cele- 

 brated German mycologist, determined to test this popular 

 idea, and inoculated wheat plants with spores obtained from 

 the fungus growing on the leaves of a barberry bush, and was 

 surprised to find the well-known rust of wheat appear in due 

 course at the points infected. Repeated experiments proved 

 that the rust of wheat and the " cluster-cups " on barberry 

 were stages of one and the same fungus. This discovery has 

 led to the reduction of numerous forms, at one time considered 

 as good species, to the condition of stages in the life-history of 

 other species. 



Thielavia basicola. — A Yorkshire fungus, although not an 

 example of heteroecism, includes three markedly different 

 stages in its complete life-cycle. In fact, the three stages are 

 structurally so distinct that they were originally placed in 

 three different genera, which belonged respectively to three 

 different families of the Fungi. More than half a century ago, 

 Berkeley discovered a fungus forming black stains on the root 

 and lower part of the stem of garden peas, and a cultivated 

 species of Nemophila. To this fungus, which proved, from the 

 standpoint of knowledge at the time, to be an undescribed 

 species, Berkeley gave the name of Torula basicola (Fig. 2). 

 Aboui twenty-five years ago I found a small, snow-white 

 mould-like fungus on the base of the stem, and on the dead 

 leaves (if Blysmus compressus in the neighbourhood of Scar- 

 borougli. This was considered as a new genus, and was called 



igog June 



