Oenothera Lamar ckiana and O. gig as . 965 
mentation of a univalent spireme, and there is no place evident in the 
reduction processes of Oenothera for the parallel conjugation of two spiremes 
(parasynapsis). 
This can be said respecting the results of the synaptic contraction. 
From the dense reticulum of the presynaptic stages there is differentiated 
a thread system, and during the process the threads are materially thickened 
and the length of the system is apparently much shortened. This history 
may indicate nothing more than a process of condensation and contraction 
of the chromatic elements of a thread system such as is found during every 
mitosis among higher plants, in which case synapsis may have little 
significance except as associated with the peculiar conditions surrounding 
the growth and activities of spore mother-cells. On the other hand the 
actual results of the synaptic contraction would certainly bring prochromo¬ 
somes or other chromatic elements into as intimate a relation or proximity, 
short of an actual homogenous mixing of substance, as could well be 
imagined by the most enthusiastic advocate for transfers or mutual inter¬ 
actions of idioplasms. The long period in which the nucleus lies in a state 
of synapsis also favours the importance of the process as one of a funda¬ 
mental nature. In the history of reduction in the Oenotheras there is 
apparently no phase when the chromosomes or their representatives 
(chromatic centres or prochromosomes) are in such intimate association 
and for so long a time as during mid-synapsis. 
We are now ready to pass to another phase of the history of reduction 
that also presents serious difficulties of observation and interpretation, and 
which must be considered with reference to later events when the chromo¬ 
somes become differentiated. This puzzling phase comprises the history 
from the period of mid-synapsis, characterized by the fully contracted 
synaptic knot, to the formation of the mature spireme which segments into the 
full number of sporophytic (somatic) chromosomes. With the loosening of 
the synaptic knot there emerges a thread system the elements of which 
are markedly thicker than the chromatic strands of the early and mid¬ 
phases of synapsis. These conditions are clearly shown in Figs. 15 and 
16 for grandiflora (Davis, ’ 09 ), Figs. 9 and 10, 42 and 43 for biennis 
(Davis, TO), Figs. 10 and 11 for Lamarckiana , and Fig. 55 for gigas. 
With the thickening of the threads there also takes place a shortening 
of the thread system, and there can be little doubt that the two processes 
are the result of the general condensation and contraction of the chro¬ 
matic material throughout the period of synapsis. The next developments 
which lead to the differentiation of the mature spireme are more difficult 
to follow, for the threads take on irregularities of form and thickness 
which might suggest various interpretations to investigators who have 
reported the stages of double threads (strepsinema) in certain material. 
The writer, however, for reasons stated below, believes these peculiarities 
