422 BASIDIOMYCETES. 



spore. The basidia originate from basidial layers or from complex 

 hymenia, produced either inside some special structure, or on 

 the surface of special sporophores, or on some definite part 

 of these. 



The group may be sub-divided into the Dacryomycetes, Hymeno- 

 mycetes, and GasteroTnycetes (including Phalloideae). Of these only 

 the Hymenomycetes contain species parasitic on plants, the others 

 include harmless saprophytes, which live in the soil, some of 

 them, however, taking part in the formation of mycorhiza. 



THE HYMENOMYCETES. 



The unicellular basidia give ofl' from their apices four (any 

 number from 2 to 6 may occur) sterigmata, from each of 

 which a single basidiospore is abjointed. The basidia arise 

 from free exposed hymenia, which generally occupy the whole 

 or part of large compound sporophores. The greatest develop- 

 ment of the sporophore is attained in the umbrellas of the 

 Agaricineae, and the large discs of the Polyporeae. It is only 

 amongst the lowest genera, like Uxohasidntm, that the basidial 

 layers are produced directly on the organs of the host, and the 

 basidia arise directly from the hyphae. 



Reproductive cells, other than basidiospores, are rare. In a 

 few cases amongst the Polypm'eae, Brefeld and others have 

 observed conidia and chlamydospores (Oidia, etc.) ; while some 

 few Agaricineae have the latter form of spore, but never conidia. 



The mycelium is of a very varied nature. It frequently 

 inhabits wood, and in many different ways brings about 

 destruction of lignified tissues. Other modifications are seen 

 in the forms of mycelium known as rhizomorphs, rhizoctonia, 

 mycorhiza, and other closely felted masses of_ various shapes, 

 which will be considered in detail as occasion requires. The 

 formation of clamp-connections is also a special feature of the 

 mycelium of the Hymenomycetes. In many cases the mycelium 

 retains its vitality and perennates for several years. 



The genus Exohasidium consists of parasites which produce 

 malformation of their host ; many of the Polyporeac and 

 Agaricineae are deadly enemies of forest and fruit-garden, 

 while as wound-parasites many of them are specially dangerous. 

 The general means of combating tliem consist in cutting out 



