372 RESEARCHES ON FUNGI 



Telemorphosis is the phenomenon in which one hypha, acting at 

 a distance, stimulates another hypha to alter its form by sending out an 

 opposing fusion hypha. 



Zygotropism is the phenomenon in which two hyphae, as a result of 

 mutual stimulation, make growth curvatures toward one another and 

 grow toward one another until they meet. 



Naturally occurring hybrids between two species of fungi are 

 unknown. However, a few hybrids have been produced artificially. 

 Thus Burgeff obtained zygospores when he crossed Phycomyces nitens 

 and P. Blakesleeanus, Dodge obtained fruit-bodies by crossing Neurospora 

 sitophila and N. tetrasperma, Hanna and Popp obtained smut spores as 

 a result of crossing Ustilago avenae and U. levis, and Flor obtained bunt 

 balls as a result of crossing Tilletia tritici and T. laevis. In all these cases 

 sexual fusions between two mycelia belonging to different species must 

 have taken place. 



In general, in Ascomycetes, Basidiomycetes, and Fungi Imperfecti. 

 vegetative fusions are readily formed between adjacent hyphae of one 

 and the same mycelium or of two mycelia of the same species ; but, as 

 a rule, they are not formed between two mycelia of two different species, 

 even when the latter belong to the same genus. 



In the Hymenomycetes the inability of the mycelia of distinct species 

 of the same genus to fuse with one another throws light on the fact that 

 in this great group of fungi (1) wild hybrids are unknown and (2) all 

 attempts to hybridise two species of the same genus have so far failed. 



In general, the occurrence or non-occurrence of hyphal fusions between 

 hyphae of two mycelia of different origin may be applied as a criterion 

 for identifying or distinguishing between species of Ascomycetes, 

 Basidiomycetes, and Fungi Imperfecti whose affinities are uncertain. 



The author has described the formation of hyphal fusions in 

 Pyrenomycetes (Pleurage curvicolla, P. anserina, Fimetaria fimicola), 

 Discomycetes (Pyronema corifluens), Hymenomycetes (Coprinus ster- 

 quilinus, C. lagopus), and Gastromycetes (Sphaerobolus stellatus). The 

 principle involved in the mode of observation was that of continuous 

 watching of a particular part of a living mycelium with a view to witness- 

 ing all those stages in growth leading up to, and culminating in, the 

 actual union of two hyphae of one and the same mycelium. 



All hyphal fusions are essentially end-to-end ones, i.e., when a hyphal 

 fusion takes place, it takes place between the end of one hypha and the 

 end of another hypha. 



Four kinds of hyphal fusions have been distinguished : (1) hypha-to- 

 hypha fusions, (2) hypha-to-peg fusions, (3) peg-to-peg fusions, and (4) hook-to- 

 peg or clamp-connexion fusions. In this terminology : by the word hypha 

 is meant an ordinary vegetative hypha of some length which has grown 

 freely in the culture medium before becoming " attracted " by another 

 hypha and undergoing growth changes leading to a hyphal fusion ; by 



