BOLETUS. 259 



up its oxygen in the form of ozone, the result being a more 

 or less intense blue coloration. 



Starch has been proved to be present in the flesh of the 

 stem and pileus of many species of Boletus. If a portion of 

 the flesh, after the blue coloration above described has 

 passed away, is touched with a solution of iodine, the blue 

 coloration characteristic of the presence of starch is at once 

 produced ; this colour disappears on heating, but returns 

 when cool ; if the starch is extracted from the fungus by 

 boiling water, and the solution mixed with a diastase (saliva), 

 after remaining for some time it loses the power of becoming 

 blue on the application of iodine, has, in fact, been converted 

 into a sugar, which readily reduces a solution of Fehling's 

 fluid or of cupro-potash. In most instances where starch is 

 present in fungi, it is in solution in the cell-wall, as in the 

 asci of many of the Discomycetes ; in the sclerotium of 

 Claviceps purpurea it is present in the form of small grains. 



Hovering round Boletus, as a typical and central genus, 

 are several genera, established as such by different myco- 

 logists. The genus Strobilomyces kept up in the present 

 book out of deference to its founder, the late M. J. Berkeley, 

 called by Fries " The Prince of Mycologists " Ls very 

 closely allied, differing in fact from Boletus only in the 

 coarsely scaly pileus. Gyrodon, founded as a distinct genus 

 by Opatowski, differs in the very short tubes with sinuous 

 openings, and is considered here as a subgenus, in which I 

 have followed Fries. Boletinus, Kalchbr., differs in the tubes 

 not leaving the flesh of the pileus by a plane surface, as in 

 Boletus, but little points of the flesh of the pileus pass down 

 into the tubes; the general aspect is, however, that of 

 Boletus, and it is included by Fries as a subgenus. The 

 only species, B. cavipes, Kalchbr., closely resembles in size, 

 habit, and colour, Boletus liiteus, being more umbonate, with 

 a well-developed whitish veil, and pores decurrent, the 

 openings rather elongated radially, and stem hollow ; this 

 species has not yet been found in Britain. Polyporus differs 

 from Boletus in the trama or dissepiments of the pores being 

 continuous with the flesh of the pileus ; hence the tubes 

 cannot be removed in a clean manner from the sporophore 

 or flesh of the pileus. 



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