726 FUNGI 



spores, most commonly four, though two, six or eight are 

 produced in some species. Such a conidiophore is spoken of 

 as a typical basidium, and its conidia, termed basidiospores, 

 arise on delicate projections designated sterigmata (Figs. 247 

 and 252). 



Two series of the Eubasidii are recognised, namely : — 

 (i) the Protobasidiomycetes 

 and (ii) the Autobasidiomycetes. 



In the former the basidia are divided transversely or longi- 

 tudinally by septa into four cells, while the latter fungi have 

 unicellular basidia. 



Series A. — Protobasidiomycetes. 



To the Protobasidiomycetes belongs an important group known 

 as ' Rust '-fungi, or Uredinece. The latter are all endophytic 

 parasites with delicate septate mycelia, generally confined to 

 small localised areas within the leaves and stems of their host- 

 plants. The basidia always originate from certain forms of 

 chlamydospores, which are termed teleutospores. Many species 

 of ' rust '-fungi are highly pleomorphic and possess several other 

 forms of spores to which special names are given. Moreover, 

 in some instances the parasite spends part of its life on one 

 kind of host-plant and subsequently completes its existence 

 upon another different host-species. Fungi in which this change 

 of hosts is observed are said to be hetermcious, the term autoecious 

 being applied to those which spend their whole life upon one 

 victim. 



7. ' Bust ' and ' Mildew ' of Wheat. — One of the commonest 

 species which is strikingly polymorphic and at the same time 

 a good type of a heteroecious fungus causes 'rust' and 'mildew' 

 on wheat. The annual loss due to this parasite in wheat- 

 growing countries amounts to several millions of pounds 

 sterling. 



