594 
Saxton.— Contributions to the 
In Pinus the two groups of chromosomes remain distinct during the 
formation of the spindle, a phenomenon also occurring in Larix (Woycicki, 
as quoted by Coulter and Chamberlain (12)), Tsuga (Murrill (35)), Juniperus 
(Noren (37), Nichols (36)), and Cunninghamia (Miyake (32)), and doubtless 
true for most, if not all, other Conifers. In Tetraclinis two distinct groups 
of chromosomes are formed, which can be made out quite plainly at the 
time when spindle fibres begin to appear. 
Figs. 50 and 51 are drawn from two adjacent sections of the same series. 
The sections did not pass medianly through both groups of chromosomes in 
the same section, but Fig. 50 is the one which includes the point of junction 
of the two groups. Fig. 51 has passed through practically the centre of the 
male group, while only outlying parts of three or four female chromosomes 
are shown. The next section on the other side shows female chromosomes 
almost solely, a few fragments only of the male being visible above. In all 
three sections, also, the spindles are distinct as well as the chromosomes. 
Juniperus is the only other genus of plants where such a segregation of 
chromosomes has been clearly proved to follow complete fusion of the male 
and female nuclei — complete, that is, as far as revealed by the highest 
powers of the microscope — and these two cases, which are probably 
duplicated in other Cupressoideae, appear to the writer to constitute 
the most important cytological evidence we at present possess in plants 
in regard to the continued individuality of male and female chromo- 
somes. To these should be added Miss Ferguson’s (17) demonstration of 
segregation in Pinus at the second division in the proembryo, a record which 
has not been repeated for any other genus of plants, but which is duplicated 
in the cleavage of the fertilized egg of Cyclops (RUckert (43)) amongst 
animals. 
A rough count of the chromosomes in these sections indicated a con- 
siderably higher number than was expected, but this was proved to be due 
to the length and very irregular shape of the chromosomes, so that not only 
does one chromosome certainly appear in more than one section in some 
cases, but almost certainly two separate parts of the same chromosome may 
appear in the same section. As it is quite impossible to trace out the whole 
length of each individual chromosome, it was assumed that the longest 
whole thread of chromatin which could be demonstrated was a whole 
chromosome, an assumption which may be considered reasonably probable ; 
this was carefully drawn and measured, making some allowance for the 
change of focus required to bring successive parts of the thread into view ; 
each piece of thread appearing in the same half (female) of the three 
sections was drawn and measured in a similar manner, and the total length 
of thread obtained in this way was divided by the length of one chromosome. 
The probable error in such an estimate might be taken at about 10 per cent., 
and the fact that the actual figure obtained was almost exactly 1 2 makes 
