967 
Oenothera Lamarckiana and O. gigas. 
each composed of two chromosomes. It is to be expected that different 
material of grandiflora will show deviations from these conditions approach¬ 
ing more closely to those of the other species, since the differences depend 
on the degree of complication in the arrangement of the portions of the 
spireme. 
It is best to approach the interpretation of the synaptic processes 
in Oenothera from the stage of the segmented spireme. We are, in the 
writer’s opinion, on safe ground in our understanding of this condition 
as the segmentation of a univalent spireme into the full set of sporophytic 
chromosomes (diploid), and any explanation of the subtle events of synapsis 
must accord with this view. Should it be established that the spireme splits 
longitudinally before its segmentation, and that this fission is quickly closed, 
the most probable explanation of such a phenomenon would be the very 
early appearance of the division which is effected during the anaphase of 
the heterotypic division in preparation for the homotypic mitosis. But, 
as previously noted, the writer has found no evidence that such a division 
takes place or that there is a fusion of parallel spiremes. There is then left 
the interpretation of synapsis as a long-continued condensation of the 
chromatic elements from^ the stages of the presynaptic reticulum to the 
spireme which develops from the thickened threads that emerge from 
the synaptic knot, the stage of mid-synapsis (synaptic knot) being charac¬ 
terized by the very close association of the chromatic elements. It is 
possible that the above view may be modified by the study of the reduction 
phenomena in Oenothera hybrids, but the evidence so far seems in its favour. 
With respect to the relations between the chromosomes in the spireme 
it is possible that they are alternately of paternal and maternal origin, 
or they may be arranged merely by the law of chance. On this point 
we shall probably have little or no evidence in Oenothera until suitable 
hybrids have been studied not only in the F x generation but also through 
selected forms of the F 2 and perhaps later generations. Whenever the 
chromosomes are associated in pairs during diakinesis it is evident that 
the members of a couple were adjacent chromosomes on the segmented 
spireme, but the phenomenon of pairing is relatively uncommon in the 
Oenotheras , and it is unsafe to lay emphasis on these conditions. Usually 
the chromosomes are distributed without apparent order during diakinesis, 
which in consequence is not so striking a stage in Oenothera as in those 
types where a regular pairing of the chromosomes obtains. The apparent 
lack of system in the arrangement of the chromosomes during diakinesis, 
however, may not be real since physiological conditions may determine 
a very precise distribution of the chromosomes by the heterotypic mitosis. 
The phenomenon of the ‘ second contraction ’ which takes place during 
the segmentation of the spireme and the condensation of its portions to form 
the sporophytic chromosomes is frequently a clearly defined phase of the 
