4 RESEARCHES ON FUNGI 



with Absidia glauca, Mucor hiemalis, etc. 1 These fusions (Figs. 5 

 and 6, pp. 13 and 14), which bring the protoplasm of the parasite and 

 host into continuity with one another, are used by the parasite for 

 abstracting nutriment from the host and are therefore vegetative in 

 function. However, if we wish to distinguish them from ordinary 

 vegetative fusions such as occur in the mycelium of most of the 

 Higher Fungi, we may refer to them as parasitic fusions . 



In a mycelium of one of the Higher Fungi, e.g. Coprinus lagopus 

 or Pyronema confiuens, growing in a dung-agar medium, the indi- 

 vidual hyphae are not at all times in the right physiological condition 

 for fusion. Young hyphae growing rapidly at the periphery of a 

 mycelium often grow close together or cross one another, and yet 

 they show no tendency to fuse with one another. Fusion first sets 

 in in the older parts of a mycelium where the culture medium is 

 becoming exhausted and, in general, the process is promoted by 

 conditions of starvation. 



In Pleurage curvicolla and other Pyrenomycetes, where two 

 hyphae run near to one another and more or less parallel to one 

 another for some distance, bridging hyphae are usually formed 

 between them at intervals along their length, so that they become 

 converted into a scalariform structure (cf. Fig. 1). Any one hypha 

 may fuse with two or more neighbouring hyphae by means of such 

 bridges. The nearer the parallel hyphae are together, the more 

 numerous, as a rule, are the bridges which come to connect them. 



The formation of one hyphal fusion at a particular place in a 

 mycelium appears to prevent the formation of other hyphal fusions 

 close by ; and, when a certain density of hyphal fusions per unit 

 of mycelium has been attained (cf. Fig. 1), no more hyphal fusions 

 are formed. As will be shown in Chapter II, there is protoplasmic 

 continuity between all the cells in a mycelium of a Higher Fungus 

 or a Fungus Imperfectus. Such a mycelium, however much 

 branched, is therefore a morphological and physiological unit, and 

 as such it should be thought of in connexion with the formation of 

 hyphal fusions. The mycelium as a whole strives, as it were, to 

 become a three-dimensional network, but a network of not too fine 



1 For more details of the parasitism of Parasitemia and Chaetocladium, as 

 determined by Burgeff, vide infra. 



