324 



COMPARATIVE MORPHOLOGY OF FUNGI 



forms maturing in the overwintering fruit, in the other representatives of 

 the subgenus Stromatinia. In the forms on Rosaceae, the conidia are 

 also formed on the fruits (often predominantly on these) so that an infec- 

 tion from fruit may take place. In this manner the fungus may spread 

 extremely rapidly, especially on stored fruit, causing the fruit industry 

 enormous losses. 



The change, here described in detail for S. Urnula, of an imperfect 

 form developing in spring on the young shoots of a host to a perfect form 

 developing in the course of the summer on the host fruit, has the possi- 

 bility of a special biological relationship, which has been investigated in 

 S. Ledi and S. Rhododendri. When in the spring the ascospores of the 



Fig. 214. — Sclerotinia cincrea. Apothecia developed in the spring from peach mummies 



(Photograph by E. E. Honey.) 



former are mature, Ledum is not yet developed; V actinium is ready, how- 

 ever, to unfold its young shoots. These are infected by the ascospores 

 which develop mycelia in them and form moniliform conidia. Mean- 

 while Ledum has bloomed, the conidia from V actinium uliginosum infect 

 the ovaries of Ledum palustre and here develop the sclerotia with which 

 the fungus overwinters. Similarly, in the spring, S. Rhododendri forms 

 its Monilia stage on the twigs and branches of V actinium Myrtillus, while 

 in summer it parasitizes fruits of Rhododendron (E. Fischer, 1926). S. 

 Rhododendri and S. Ledi, as the Claviceps on Brachypodium silvaticum, in 

 the Hypocreales, need two hosts for the completion of their life cycle; 

 Vaccinium Myrtillus and V. uliginosum for the imperfect forms and 

 Rhododendron ferrugineum and R. hirsutum and Ledum palustre, respec- 

 tively, for the perfect forms. Thus they are heteroecious, even if not in 



