284 RESEARCHES ON FUNGI 



(a) mycelium ayid the {a) nuclei move alo7ig the hyphae of the 

 {A) mycelium, and the moving nuclei undergo division and make 

 their way to the places where the rudiments of the aecidia are 

 being formed ; so that, in the hyphae which form the aecidial 

 rudiments, both {A) and (a) nuclei are present. These hyphae 

 now form a series of uninucleate cells, some of which contain an 

 {A) nucleus and some an {a) nucleus. Then the co-operation of 

 {A) and {a) cells by means of nuclear migration or cell fusion sets 

 in, and this leads to the formation in each aecidium of a spore-bed 

 in which the basal cells contain conjugate nuclei {A)-\-{a). 



In Hypothesis No. 2, the assumption that the {A) and (a) 

 mycelia do not mingle appreciably in each other's original pustules 

 is based on the fact that, in the Hymenomycetes, when two haploid 

 mycelia of opposite sex are placed near together on a nutrient 

 medium, on meeting with cne another they do not intermingle 

 appreciably. The non-intermingling of the {A) and {a) mycelia 

 may be attributed to the exhaustion of the host-leaf locally by 

 both the [A) and the (a) mycelia ; so that {A) hyphae, on coming 

 into contact with the (a) mycelium, cease to grow in length and 

 {a) hyphae, on coming into contact with the {A) mycelium, also 

 cease to grow in length. 



The following assumptions of Hypothesis No. 2 are based on 

 what is known of the diploidisation process in the Hymenomycetes : 



(1) that the {A) and the (a) mycelia, on coming into contact with 

 one another, unite by means of one or more hyphal fusions ; 



(2) that one or more {A) nuclei move through one or more hyphal 

 bridges into the (a) mycelium where they divide and lind their 

 way to the localities where the (a) mycelium is forming aecidial 

 rudiments ; and (3) that one or more (a) nuclei move through one 

 or more hyphal bridges into the [A) mycelium where they divide 

 and find their way to the localities where the {A) mycelium is 

 forming aecidial rudiments. 



The assumption in Hypothesis No. 2 that the hyphae which 

 form the rudiments of the aecidia at first contain both {A) and {a) 

 nuclei, but subsequently undergo cell-division so as to produce a 

 mass of uninucleate cells of which some contain an {A) nucleus 

 and others an {a) nucleus, has been made in order to account for 



