Chromosomes in Pollen Mother -cells. 
343 
or female pangens or those bearing other distinct qualities. It seems 
reasonable also that the sexual differentiation observed in certain moulds 
(Blakeslee, ’06) may be explained in a similar manner. 
In conclusion, I think it is not mere speculation to assert that in plants 
of a low degree of differentiation, the hereditary determinants or pangens 
are correspondingly much less specialized ; but as differentiation along the 
lines of both vegetative and reproductive structures and functions became 
more and more pronounced in phylogenetic development, it is only reason- 
able that the pangens should undergo a corresponding differentiation. 
And in the higher organisms where certain sharply defined and fundamental 
characteristics appear, as, for example, those of sex, it follows that these 
important and fixed characteristics should be represented in the hereditary 
substance by pangens that are as distinct and as sharply defined from other 
pangens as the characters in question are different from all other characters 
of the individual. The question then to determine is whether such pangens 
are equally distributed among all the chromosomes, or whether any of the 
chromosomes are qualitatively different. To arrive at any trustworthy 
conclusions, it is necessary that experimental studies carried out with this 
end in view must go along with a cytological study of the chromatin. 
Summary. 
The resting nucleus of the pollen mother-cell consists of a linin net in 
which the chromatin is held, either in the form of very fine granules of 
uniform size, or in larger aggregations or lumps which are composed 
of smaller granules. The chromatin granules or lumps are often evenly 
distributed within the nucleus ; frequently there is a tendency toward 
a peripheral arrangement of the chromatin, leaving the centre freer from 
the granules or lumps. One or more nucleoli are present. Prior to 
synapsis there may be formed, in some cases in Lilium Martagon , a very 
delicate, spirem-like threadwork in which the chromatin occurs as a single 
row of small chromomeres ; in other cases the chromatin did not seem to 
become so finely divided, the nuclear framework, with larger chromatin 
lumps, passing directly into synapsis. 
Synapsis consists in the contraction of the entire nuclear threadwork 
into a compact and dense ball, which usually lies close to the nuclear 
membrane. The position of the contracted mass in the nuclear cavity 
does not seem to be determined by gravity. The nucleolus may or may 
not be included within the contracted mass. The contraction of synapsis 
represents the longest pause in the mitotic process. There is no union of 
two spirems in synapsis. 
The synaptic mass on loosening up forms the hollow spirem, which is 
double, being due to a longitudinal splitting and not to the lateral union of 
two spirems. In Podophylhmi the loose spirem is of a uniform thickness 
c c 2 , 
