Chromosomes in Pollen Mother-cells. 
313 
is stated to occur just before synapsis, a thicker chromatin thread is shown 
than in his Fig. 56, which is in synapsis. If Overton’s Fig. 56 correctly 
represents the chromatin thread in synapsis, it seems to me that his Fig. 55 
is a loosening up of the synaptic mass, and hence a later stage, for I have 
found no such condition as his Fig. 55 before synapsis. 
Cardiff (’ 06 ) claims that, previous to synapsis in Acer platanoides , 
Salomonia bijlora , Ginkgo biloba , and Botrychium obliquum , there are 
formed two or more chromatin threads which arrange themselves in pairs 
longitudinally and move together as synapsis approaches, finally fusing in 
synapsis. Judging from his own experience in the study of nuclear pheno- 
mena, the writer is of the opinion that Cardiff’s figures are too diagrammatic 
to enlist confidence in the accuracy of his interpretation. 
Both cell and nucleus increase rapidly in size, so that when synapsis is 
complete they have about reached their maximum dimensions. In Podo- 
phyllum the pollen mother-cells vary considerably in size, as do also the 
stamens in any given flower. In thicker and longer anthers larger cells are 
found, but whether this is always true no effort was made to determine. It 
is very frequently true, however, that the cells near the middle of the anther 
may be very much longer than broad. Fig. 6 represents a cell which 
is larger than the average. 
Whether the chromatin undergoes any marked change from that 
shown in Figs. 1-4 before contraction, as will be pointed out below for 
Lilium , cannot be stated positively. With the rapid increase in size of the 
cell and nucleus, the entire contents contract or ball up toward one side of 
the nucleus. This contraction is a rapid process, and whether the rapid 
growth of the nucleus is a stimulus to this contraction is an interesting 
question. The nucleolus may be included partly or wholly within the con- 
tracted mass, or it may lie merely in contact with it, or entirely free and 
at a remote side of the nucleus. As a rule, the nucleolus is included within 
the chromatin mass (Fig. 5). When complete synapsis is reached, the mass 
is tightly balled up, many nuclei showing no free portion projecting into 
the nuclear cavity. Frequently a few shreds of linin, including some 
chromatin, protrude from the mass, and sometimes a small portion of the 
chromatin thread may project. In some cases very fine delicate threads 
extend from the mass across the nuclear cavity to the nuclear membrane. 
There seems to be little or no regularity in the position of the synaptic 
mass in the nucleus as regards the upper or lower ends or the sides. 
Cardiff states that in the plants studied by him gravity determines the 
position which the mass shall take. This explanation does not hold for 
Podophyllum or Lilium. 
In the contracted mass no definite structure can be made out. Some- 
times the appearance is that of a balled-up mass of lumps or granules, and 
sometimes that of a chromatin thread. The nuclear membrane in the 
