466 
Keene . — Cytological Studies of the 
In the material at hand, however, these plastids have been found at various 
stages in material from six to twelve weeks old. In most of the zygo- 
spores a single plastid appears, and in year-old zygospores only one large 
plastid is usually found, although several small ones may be present. In 
some instances at this age, the amber-coloured oil substance has disappeared 
and only the plastid remains. This would seem to be a further indication 
that the oil is a reserve food-substance. In many of the zygospores at the 
end of a year, there appears to have been no change, and they appear 
exactly as they did at the end of eight weeks. 
According to Miss McCormick, the large structures which she finds 
associated with the nucleus have been identified by Stevens as similar to 
the coenocentrum described by him in Albugo, Miss McCormick describes 
this in Rhizopus as arising at the point of contact of the suspensors before 
the gametangia are cut off. This may be similar to the zonation described 
in Sporodinia. 
Various writers have described the presence of coenocentra in the 
Fungi, and also the occurrence of oil. 
Wager (35), in 1896, on Cystopus candidus , describes the presence of 
a coenocentrum and says, in connexion with the formation of oil, ‘ Small oil 
droplets in considerable numbers are to be found. These oil drops 
gradually fuse together, and at certain stages one large oil drop with 
a number of small ones is to be seen. . . . All the oil drops gradually fuse 
together into a somewhat irregular lumpy mass, and finally into the large 
central oil sphere of the ripe oospore.’ 
Wager (36), in J900, in studies on Peronospora , describes the presence 
of a dense granular mass in the centre of the oosphere, which becomes 
converted into a homogeneous ill-defined body. This central body appears 
to play some part in bringing the sexual nuclei together. 
Davis (14) describes a coenocentrum in Albugo Candida. It is described 
as being composed of deeply staining, slightly granular protoplasm. ‘ It is 
sometimes surrounded by a zone of lightly staining protoplasm through 
which delicate radiations may be traced. Later the structure contracts 
somewhat, rounds itself off, and becomes a very dense body with a firm 
outline.’ In a later paper, Davis (15) describes coenocentra associated with 
the nuclei of the eggs in Saprolegnia. 
Stevens (29), in 1901, summarizes briefly his own observations on the 
structure of the coenocentrum. He studied A. Portidacaceae , A. Tragopo - 
gonis , and in an earlier paper (1899) A. Bliti . He says, ‘ In A. Portulacaceae 
the coenocentrum is the least developed, consisting simply of a zone of 
darkly staining cytoplasm which contains at its centre the alveolar region. 
In A. Bliti the structure is more prominent owing to the presence of 
a distinct central globule. In A. Tragopogonis the central globule seems 
to be formed by the trophoplasm of the central region, or rather by the 
