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Page number:115 
Remarks (internal):The Cottony type is the commonest and most rapidly growing of the three types; the majority of the cultures grow 44-65 nun in two weeks, while the Zonate type grows about 41 55 mm, and the Marmorate type 37-45 mm in the same time. These types seem to have no correlation with the species of the host tree. Cultures from Betula generally grow somewhat more rapidly than those from Salix and Alnus glutinosa, while the average growth rate of the others is still lower.
Neither do the three culture types seem to correlate with the varietal division of P. igniarius, which must be based on other than cultural characters.
The Cottony type of P. igniarius and P. nigricans corresponds in many ways to the Bleaching type of P. tremulae and P. populicola, and the Zonate type to their Staining type. There-fore, when the growth rates of P. tremulae and P. populicola are compared with those of P. igniarius and P. nigricans, comparisons should be made between the Bleaching and Cottony types, and the Staining and Zonate types. However, the difference between the Cottony and Zonate types is far less profound than that between the Bleaching and Staining types, and is farther obscured by numerous intermediary cultures. and the existence of the Marmorate type in P. igniarius.
The developmental mechanism of these different cultural types is unknown.
No reliable differences were found between the cultures of P. igniarius and P. nigricans. The slight differences in growth rate and other measurements are evidently caused by the smaller material of P. nigricans. Core setae were found only in the cultures of P. populicola, but even there only in a few cases. As they occur in the fruit bodies of all three species, their presence versus absence in culture can hardly be a specific character. The special thick-walled cells common in the Marmorate and Zonate types of P. igniarius are also found in P. nigricans, P. populicola and P. lundellii though in much smaller amounts.
Although wide morphological variation exists between the different strains of P. igniarius, it is interesting to note that different isolations from a fruit body can be very constant. In 1967. an isolation (Niemeld 159) was made from a certain carpophore, and in 1972 again from the same regrown fruit body (Niemeld 455). Both strains represent the Marmorate type. and resemble each other extremely closely in all respects, including rate of growth and the complicated colour pattern. The same phenomenon was observed in other cases, too. These observations also show that storing cultures for 5 -8 years does not affect their growth characters.
Dried cultures of the following strains are kept in H, under P. igniarius:
Cottony type: Laine & Niemelä 221, 257; Niemelä 448 Zonate type: Niemelä et al. 220; Kaivos 253; Mäkinen & Niemelä 481
Marmorate type: Niemelä 159, 335 (Poland), 455
The descriptions of cultures of P. igniarius given by American authors correspond well with the present results, when those for P. tremulae (Fomes igniarius var. populinus) are excluded (Campbell 1938, Nobles 1965. Verrall 1937).
 
Description type:Culture description 
Description:The cultures grow rapidly; at 24°C radial growth is (16-) 20-30 mm in a week and (35-) 40-65 mm in two; 50% of the cultures cover the dishes in three weeks, 37% in four weeks, 8% in five weeks and 5% in six weeks. (Figs. 25-28).
Great changes occur in the cultures with age, and there is rather wide variation between different strains and isolates.
After one week, the majority of the cultures form thick cottony mycelium, which is azonate, white or with diffuse yellow, cream or ochre colon ration at the centre. Some cultures produce thinner mycelium with a translucent, bleached outer half, changing gradually to a brown centre, and only low aerial mycelium.
After two weeks of growth, three culture types can be separated: the Cottony type (50-70%), Zonate type (20-30%) and Marmorate type (10-20%), often with intermediary forms. The mycelium of the Cottony type is thick, aerial, loose, even or tufty, mostly azonate, not translucent even at the margin. The colours fade from Buff, Yellow ochre and Cork at the centre via Maple or Maize, to a cream or white margin. The culture of the Zonate type has a sharply delimited centre with distinct zones of Leather, Gold brown and Burnt umber, with Buff in between. The margin is 1-2 cm wide, discoloured, semi-translucent. The aerial mycelium is low, almost absent in some of the zones, and submerged mycelium is correspondingly dominant. The Marmorate type possesses a bleached, translucent margin, which changes gradually to a brown centre with patches of dark brown submerged mycelium and lighter brown low aerial mycelium, some of them crustose.
The one-month-old cultures show the same division into three types. The Cottony type is even or densely tufted, aerial, Cinnamon, azonate and cottony to felty in texture. The Zonate type has the least aerial mycelium, especially at the margin, which is Sepia. Chocolate or Burnt umber, the centre being covered with low aerial mycelium, Cinnamon to Gold brown in colour. The Marmorate type is the most showy one, possessing a very low appressed mat of aerial mycelium that covers the whole Petri dish, with sharply defined zones and patches of Cinnamon, Toast, Gold brown and Umber, and almost black crustose lines.
The advancing zone contains generative hyphae, which are thin-walled, 1.5-4 µm in diam., hyaline, with simple septa and rather few branches.
Old mycelium of the Cottony type contains generative hyphae 1.6-4 µm in diam., and very densely packed flexuose skeletals, which are yellowish brown, 1.3 2.9 µm in diam., mostly aseptate and very seldom branched. Coils of the skeletal hyphae are common, 20-25 µm in diam.
The Zonate and Marmorate types are more variable in the microscope. The generative and skeletal hyphae are as in the Cottony type. Darker brown thickened cells are common, 60-100 ( 300) x 4-6 . µm, joined at both ends to generative hyphae, with reddish brown, 0.8-2 µm thick walls. The amount of these cells varies greatly, and they are most common in low aerial mycelium of the Marmorate cultures. In structure they resemble setal hyphae very much, but they are not terminal formations, as setae are normally regarded to be. The crustose areas contain some skeletals, and abundant generative hyphae, from which the dense palisade of inflated branches arises. The inflatations of the crustose hyphae are 8 -17 p.m in diameter. The submerged hyphae are mainly generative, 2-6 µm in diam., with thin, hyaline walls and granulose contents, and a rather irregular shape.
All types give a positive Bavendamm reaction on gallic acid agar medium.
Species Code:
2. 6. 8. (10.) 26. 32. 37. 38. 30. 43.-44. (45. 46.) 54. 58.
 
Taxon name: