CHAPTER XXVI 

 POLYPORALES 



The Polyporales include the gymnocarpous stage of the Chiastobasidio- 

 mycetes and ascend from simple forms with a hymenium which is spread 

 out over the substrate in an arachnoid layer without definite margins 

 to resupinate crusts, to typical pileate fungi, and finally form the starting 

 point for the angiocarpous line of development which attains its maximum 

 in the stink-horns of the Gasteromycetes. 



The hymenophore is always on the outside and, in the simpler forms, 

 is smooth. In the higher groups, it forms anastomosing wrinkles, folds 

 or lamellae, which sometimes have shallow grooves between them, some- 

 times deep, tubular or elongate cracks or holes. In the highest forms, 

 it is generally divided into pores which have given the scientific 

 name, Polyporales. 



The hymenia, in contrast to the Agaricales (except Lactariaceae), 

 are often formed in youth when the hymenophore is still smooth. With 

 the development of folds and tubes, new and younger elements are always 

 added laterally. Similarly, in a given zone, they develop successively 

 rather than simultaneously, so that old and young basidia are inter- 

 mingled. In many species with perennial fructifications, in each growing 

 period a new hymenophore is laid down over the old hymenium, so that 

 these are equivalent to annual rings of vascular plants. 



In contrast to those of the Cantharellales, the basidia (Fig. 340) 

 are very regular in their structure and generally have four spores. By 

 maturity they become more or less clavate without noticeable elongation, 

 the spindles of all the nuclear divisions lie transversely at the same 

 height near the tip, mostly directly under it (chiastobasidial type). The 

 diploid nucleus divides only twice so that the young basidium is generally 

 quadrinucleate. A third nuclear division appears rarely or not at all; 

 possibly it is removed to the spore whose nuclei generally divide in 

 the young stage. This division, however, is not always completed. 



As imperfect forms, oidia are known in many genera, in some also 

 gemmae and typical conidia. 



The Polyporales contain over a hundred genera with several thousand 

 species; they include heterogenous types which in their extremes are 

 very characteristic but pass through numerous intermediate forms retro- 

 gressively toward ancestral types. Therefore systematic classification 

 cannot be accomplished according to fundamental characters, but only 



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