200 RESEARCHES ON FUNGI 



hymenomycetous origin in which (1) the mycelium has become 

 adapted to a watery habitat by budding, and in which (2) the original 

 fruit-body along with its symmetrical four-spored basidia has been 

 lost ; but in which (3) the original mode of development and dis- 

 charge of the basidiospore into the air has survived. 



In addition to basidiospores the Uredineae and the Hymeno- 

 mycetes produce conidia. We may therefore enquire whether or 

 not any of these conidia resemble basidiospores in being violently 

 discharged by the drop excretion mechanism. 



The Rust Fungi, in addition to basidiospores (sporidia), produce 

 aecidiospores, pycnidiospores, uredospores, and teleutospores. The 

 aecidiospores, as set forth in Volume III, 1 are violently discharged 

 from the aecidia, but not by the drop-excretion mechanism. The 

 pycnidiospores are not shot into the air, but are merely abstricted 

 from their pedicels into a drop of nectar. The uredospores are 

 abstricted from their pedicels into the air, but without violence, in 

 consequence of which they form a loose powder on the outside of 

 each uredospore pustule. The teleutospores, as a rule, are not 

 dispersed at all, but remain attached to their pedicels until 

 they germinate. In the Rust Fungi, therefore, the drop-excretion 

 mechanism is characteristic of only one of the possible spore forms, 

 namely, the basidiospores. 



The Hymenomycetes, in addition to basidiospores are known to 

 produce oidia, conidia, and so-called secondary spores. The oidia 

 which are formed by the breaking up of haploid mycelial hyphae 

 into smaller units, are often produced at the surface of the culture 

 medium in little projecting chains or balls. Each ball of oidia in 

 Coprinus lagopus (cf. Vol. IV, Fig. 114, p. 198), etc., is held together 

 above the surface of an agar or other culture medium by a drop of 

 fluid. My observations on the oidia of various Hymenomycetes, 

 made whilst studying heterothallism experimentally, have con- 

 vinced me that oidia are never violently discharged into the air. 

 Tiny conidia, which we may refer to as microconidia, as Brefeld 2 

 has shown, are produced on germinating basidiospores or on branches 

 of the mycelium derived from a germinating basidiospore in Auricu- 



1 These Researches, Vol. Ill, 1924, pp. 552-559. 



2 0. Brefeld, Untersuchungen iiber Pilze, Heft VII, 1888, Taf. IV, Figs. 4-8, 11. 



