CHAPTER XXXII 



AURICULARIALES 



This order includes an ontogenetic series which ranges from forms 

 without well-developed fructifications to those with characteristically 

 gymnocarpous or angiocarpous structures. In most genera the hyphae 

 secrete a gel and are able to withstand great changes in temperature and 

 moisture. In some genera which lack this gel, the zeugites develop to 

 special organs of protection called sclerobasidia. The Auriculariales fall 

 more or less definitely into three families: the Auriculariaceae, Septo- 

 basidiaceae and Phleogenaceae. Their characters will appear in the 

 following discussion, while their probable relationships are shown in the 

 diagram on page 613. 



Auriculariaceae. — This family is gymnocarpous; it develops from 

 primitive arachnoid forms in which the basidia arise directly on the 



diffuse, flocculent mycelium to those with bracket 

 fructifications, very much as we have seen in 

 the Corticiaceae. 



The primitive stage is suggested by Helico- 

 basidium (Stypinella) . The white, clamp-bearing 

 hyphae intertwine to a loose felt where they 

 radiate and end usually in small, four-celled 

 basidia which project above the felt. The sterile 

 mycelium of H. purpureum has long been known 

 as a plant pathogen under the name Rhizoctonia 

 Crocorum (R. violaceum) (Buddin and Wakefield, 

 1927). The mycelium in the vicinity of the 

 fructification is binucleate. The fusion nucleus 

 remains until the basidia have assumed their 

 crozier form. Subsequent nuclear division was 

 not observed but the basidium divides into four uninucleate cells by 

 transverse septa. During spore formation, these nuclei divide, producing 

 binucleate spores and mycelium. Since some uninucleate strains of 

 Rhizoctonia Crocorum are known, it is not clear whether these strains 

 belong here or whether the last nuclear division fails to occur. On 

 germination the spores produce a branched, purplish mycelium and binu- 

 cleate conidia, belonging to the Imperfect form-genus Tuberculina. On 

 germination of the conidia, both nuclei pass out into the mycelium. 

 In the Brazilian H. orthobasidion, the hyphal cell which bears the 

 basidium (Fig. 359, z) shows a tendency to assume a definite form when 



540 



Fig. 359.- — Helicobasi- 

 dium orthobasidion. Show- 

 ing clamps and basidia. 

 ( X 330; after Moller, 1895.) 



