308 
Notes. 
type division; the chromatin becomes aggregated to one side, constituting the 1 first 
contraction figure ’ of Farmer and Moore. This is followed by the appearance of 
a more loosely coiled spireme in each nucleus, and, here and there, longitudinal fission 
of the thread may be seen. 
At this stage the ascus-nuclei fuse. 
The longitudinal split now becomes more evident, but later it disappears for 
a time as the fusion-nucleus passes into synapsis. 
The subsequent stages of the first and second divisions in the ascus are in 
agreement with those described by Farmer and Moore for the spore-mother-cells of 
Osmunda regalis ; as the nucleus passes out of synapsis, loops become obvious, each 
of which represents a bivalent chromosome. The chromosomes divide transversely in 
the first mitosis and, in the second, the longitudinal fission begun in the first prophase 
takes effect. In each of these divisions the number of chromosomes is sixteen. 
This number was first observed, in Humaria rutilans , in 1904-5, by Guillermond, 
who also noted the occurrence of a longitudinally split spireme, and of a synapsis in 
the first division. 
In the prophase of the third division sixteen bent chromosomes appear, but in 
the anaphases only eight chromosomes pass to each of the daughter-nuclei. 
The spores are delimited by radiations passing out from the centrosome, but the 
direction of these is, to some extent, regulated by the position of neighbouring 
vacuoles, which may also aid in the delimitation of that part of the spore remote 
from the nuclear beak. 
The processes observed in connexion with the development of the ascus suggest 
the following interpretation : — 
The sporophytic number of chromosomes, as seen in the ascogenous hypha, is 
sixteen. 
The ascus, when first formed, resembles other cells of the mycelium in being 
multinucleate \ Each -of the nuclei, typically two in number, of the ascus enters 
independently on the meiotic phase. Fusion then takes place, the two spiremes 
becoming indistinguishably mingled. 
The sixteen chromosomes which appear in the first and second divisions, and in 
the prophase of the third, may be regarded as representing two sets of post-meiotic 
(or gametophytic) chromosomes united within one membrane, half having been 
derived from each spireme. 
On the spindle of the third division the chromosomes separate away from each 
other, and the true gametophytic number, eight, becomes apparent. The premeiotic 
(or sporophytic) number is restored by the apogamous fusions in the hypothecium. 
It seems not impossible that the fusion of the nuclei in the young ascus is due 
to their close proximity at a time when the nuclear wall is disappearing. A probably 
similar fusion has been several times observed between two of the four nuclei present 
in the ascus after the second division. The fusion in the ascus would be thus in no 
sense sexual, having been, moreover, preceded by a sexual fusion, in this case reduced. 
It_appears comparable rather to the fusions of sporophytic nuclei artificially induced 
by Nemec in root-tips. 
H. C. I. FRASER. 
1 Asci containing more than two nuclei were occasionally observed, but their fate could not 
be determined. 
