680 _ TRANSACTIONS OF SECTION K. 
Recent investigations * have shown that these two successive fusions are 
compensated by two reducing divisions, the sexual fusion by a meiotic 
reduction such as is associated with fertilisation in other organisms, the 
fusion in the ascus by the simpler brachymeiotic process. 
Brachymeiosis differs from meiosis in several particulars; the most 
essential seems to be that in meiosis the chromosomes are united two and 
two to form gemini; whereas brachymeiosis may be accomplished (Hwmaria 
rutilans, Lachnea stercorea) without visible union of the chromosomes, and 
even when pairing takes place (Ascobulus furfuraceous, Humaria granulata) 
the opportunity for an interchange of material seems less than in meiosis. 
It thus appears possible to differentiate between sexual and asexual fusion 
by a study of the subsequent reduction processes. 
The paternal and maternal allelomorphs and also the allelomorphs 
which are brought together by the asexual fusion in the ascus show very 
various degrees of association. Sometimes (Humaria rutilans, &c.) they do 
not become paired before the reducing division, sometimes they unite 
(Phyllactinia,? Humaria granulata, &c.) at an earlier stage. Variations 
in this respect are not confined to Ascomycetes. 
6. The Nucleus of the Yeast Plant. By Haroup Wacer, F.R.S., and 
Miss ANNIE Pentston. 
In living yeast cells in healthy condition there is always present a 
well-marked vacuole containing one or two bright refractive granules which 
exhibit a brownian movement. 
This vacuole, together with a homogeneous, stainable body, the nucleolus, 
in close contact with it on one side, is the nucleus of the Yeast cell. 
The examination of well-stained specimens, under high powers of the 
microscope with suitable illumination by means of a good substage con- 
denser, shows that there is in contact with the nucleolus and intimately 
connected with it a more or less well-developed granular chromatin net- 
work, which occurs mainly at the periphery of the vacuole. 
The nucleolus and nuclear network contain nuclein, as is shown by 
their reaction towards stains and various reagents, and both contain 
organic phosphorus and masked iron, as shown by the reactions given by 
Macallum. 
Immediately outside the nucleolus, in close contact with it, and in the 
cytoplasm immediately adjacent, we often find numerous chromatin 
granules. These also give the phosphorus and iron reactions. 
The nucleolus varies very considerably in its capacity for stains ; some- 
times so deeply stained that it seems to form with the chromatin granules 
around it a single irregular stellate-looking mass, at other times so 
slightly stained as to be almost invisible. At such times we generally 
find at the periphery of the nucleolus a single deeply-stained granule in 
close contact with it or embedded in its substance. 
The nuclear vacuole exhibits great variation in its capacity for 
stains. The chromatin granules are sometimes present in large quantity, 
sometimes almost completely absent. The amount of chromatin appears 
to vary with the state of metabolic activity of the cell. 
The prominence of the nuclear vacuole at certain stages suggests the 
possibility that it plays an important part in the metabolic activity of 
the cell, possibly in the elaboration of chromatin. 
The cytoplasm often contains bright refractive granules which are 
visible in the living cell. Some of these are composed of a fatty substance, 
! Fraser, 1908 ; Fraser and Welsford, 1908 ; Fraser and Brooks, 1909 
? Harper, 1905. 
