Humaria rutilans , Fries. 
49 
been adduced by Noll (36), and we may hope here to obtain some 
knowledge of the effect of this method of chromosome distribution in 
heredity. 
In Phyllactinia the number of chromosomes, or chromatin strands 
radiating from the central body, is the same throughout the life history 
of the fungus. On the fusion of the sexual pronuclei these strands combine 
in pairs ; thus the diplocytic nuclei contain not 1 n chromosomes, but n 
bivalent chromosomes. A similar process takes place in the fusion in the 
ascus, and the eight chromatin strands of the definitive nucleus are thus re- 
garded by Harper as tetravalent and as actually representing thirty-two 
somatic chromosomes. The meiotic divisions 1 then take place and four 
nuclei are formed ; each contains eight bivalent chromosomes representing 
sixteen somatic chromosomes. In the third division the valency of each 
chromosome is again halved and eight somatic chromosomes appear. 
The essential facts are thus the same in Phyllactinia and in Hiimaria 
rutilans. In each a sexual fusion takes place (normal in Phyllactinia , much 
reduced in Humaria ), and the actual number of chromosomes is thus 
doubled. Owing to the association of the chromosomes in pairs, the 
apparent number remains unchanged in Phyllactinia ; in Humaria sixteen 
chromosomes, the premeiotic number, can be counted in the ascogenous 
hyphae. In each case a fusion of two nuclei takes place in the ascus, resulting 
in the association, in Phyllactinia , of eight tetravalent chromosomes within 
one membrane, in Humaria , no doubt, of thirty-two univalent chromosomes. 
Meiosis occurs and four nuclei are formed, each of which, in the next pro- 
phase, shows, in Phyllactinia eight bivalent chromosomes, in Humaria 
sixteen univalent chromosomes, the reduced number for two nuclei. In 
the third division a further reduction occurs, compensating, no doubt, the 
fusion in the ascus, and in each of the two species eight univalent chromo- 
somes are shown in the anaphase. 
It may be suggested that, once a third division, compensating the 
fusion in the ascus, had been established, the latter would become a neces- 
sary process, and this may account for the extraordinary regularity of the 
appearance and fusion of the two nuclei, just as the occurrence of meiosis 
is held to render imperative some form of reduced fertilization if the normal 
sexual process be lost. 
An interesting transition between the two arrangements detailed above 
perhaps occurs in Pustularia vesiculosa as described by Maire (33). He 
states that eight chromatin bodies appear in the prophase of each of the 
three divisions, but unite into four as they pass on to the spindle. In the 
first anaphase separation occurs on the spindle, so that eight chromatin 
1 Harper did not observe a first contraction of the chromatin in the heterotype prophase; the 
absence of this stage may probably be connected with the early pairing of the chromosomes. 
