July, 1922] 
CLELAND — OENOTHERA FRANCISCANA 
393 
assurance at this stage that a fusion of the approximating threads will 
result. The condition is sufficiently different, however, from the typical 
resting condition to be noticeable and to indicate that the nucleus is ap- 
proaching prophase. 
The Heterotypic Prophase 
The series of events which follows may be briefly defined as a process 
by which a small-meshed reticulum composed of many thin, often more 
or less unevenly granular threads becomes transformed into a large-meshed 
reticulum composed of fairly thick and uniform threads — a network of 
such large mesh, and with the threads joined to each other in so few places, 
that it can perhaps be better described as a spireme. The problem before 
us for the moment is to determine by what means this change, with the 
consequent reduction in the number of threads, is brought about. 
The researches of Gregoire and Allen and their followers, on the one 
hand, and of Farmer, Digby, Mottier, and others on the other, have been 
in agreement as indicating that a most important element in this process 
is a side-by-side approximation and fusion of threads in early prophase, 
thus reducing the number of threads to approximately one half. For every 
thread there is a counterpart in the reticulum, which is so placed that 
the two can approach each other and fuse. The interpretations placed 
upon this process, however, by the two schools have been different. The 
former group (the parasynaptists) consider that the threads which enter 
into the fusion are homologous parts of two spiremes, one of which traces 
its ancestry back to the egg, the other to the sperm. The threads represent 
whole chromosomes and their fusion results in a bivalent spireme. A 
typical telosynaptic interpretation has recently been set forth very clearly 
by Miss Digby in her paper on Osmunda (1919). According to this view, 
the individual threads are half-chromosomes which form on ''association" 
a univalent filament, the chromosomes descended from both sperm and 
egg forming a part of one spireme. Miss Digby has described in the last 
telophase before the heterotypic mitosis a longitudinal fission of the chromo- 
somes into two parallel threads, which are later obscured in the resting 
stage. The parallelism in prophase she considers as due merely to the 
return of these two split parts together. According to this view, the 
fission in telophase is preliminary to the separation of chromosomes during 
anaphase of the homoeotypic mitosis. According to the Gregoirean inter- 
pretation, the two parts which fuse in prophase will separate during ana- 
phase of the heterotypic mitosis. 
While in general the method of development in Oenothera franciscana 
is telosynaptic, we shall nevertheless see that there is no evidence of any 
very general parallelism and side-by-side fusion of threads in early prophase 
such as has been observed in Osmunda. It is true that some parallelism 
is apparent at the very beginning of prophase, as I have already pointed 
out, and without doubt a certain part of the condensation of the network 
