CHAPTER VIII 

 ECOLOGY OF FUNGI 



As fungi are either saprophytes or parasites, their Kfe history is 

 bound up with the substratum on which the saprophytes are found and 

 with the host plant upon which the parasite hves, yet there are many 

 diverse forms of saprophytic fungi and the greatest variety of fungous 

 parasites. Of special interest in connection with the ecology of fungi 

 are the organs by which various fungi are tided over periods of drought, 

 inclement seasons, or during the winter's cold. These organs are 

 compacted masses of hyphse of a rounded, globular, or ellipsoidal form 

 ranging in size from those that are almost microscopic to those which 

 are the size of a small canteloupe. These tuber-like masses of hyphae 

 in a resting state are known as sclerotia (Gr. ayXupos, hard). They 

 are found in a great many fungi, as commonly in the ergot, Claviceps pur- 

 purea, a.nd the lettuce drop, Sclerotinia libertiana, which forms sclerotia 

 that may reach a length of 3 cm. in exceptional cases. These sclerotia 

 are obtained readily in culture tubes with beerwort agar, or glucose agar, 

 as culture media. From the sclerotium later arises the stalked fruit 

 body, or apothecium. Cordyceps militaris is a fungus which attacks 

 the larva of insects. Its mycelium penetrates the insect's body and 

 later in the Isaria form produces aerial hyphas which cut off conidio- 

 spores. The growth of the mycelium is such as to penetrate to all parts 

 of the larva filUng it up as if it were stuffed with cotton. 



The mass of hyphae is converted into asclerotiumand the larval body 

 is mummified, but still retaining its original external form. Later, the 

 next spring, a stiff-stalked stroma arises with an enlarged extremity in 

 which the perithecia with their asci- and ascospores are formed. Later 

 the needle-shaped ascospores are set free and by cutting off conidio- 

 spores reproduce the disease. Cordyceps (Torrubia) ophioglossoides is 

 parasitic upon an underground truffle, Elaphomyces muricatus, Fig. 

 21). The stroma is erect, yellow and club-shaped at the extremity. 

 Perithecia, asci- and ascospores are borne in the swollen part of the 

 stroma. The fungus which discharges its spores above ground finds the 



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