Io BOTANICAL GAZETTE [JANUARY 
forming heterotypic chromosomes in Fucus (YAMANOUCHI 17) 
is different; the threads seemed to indicate no association at the 
beginning of early prophase, and even after they become tangled in 
a mass at synapsis parts of them seem to be single. In the post- 
synaptic stage a reduced number of loops is formed from the threads. 
Evidently the bivalent chromosomes are formed from the two associ- 
ated arms of each loop. Unless there be some failure in observation, 
there must be two ways of forming heterotypic chromosomes. If 
the association of parental chromosomes occurs in the regularly 
formed chromatin threads in synapsis, the end-to-end hypothesis, 
held by FARMER and Moore (2), SCHAFFNER (13), MOTTIER (10), 
STRASBURGER (16), and others, seems to be the correct interpretation. 
Probably there may be more than one series of details in mitosis, 
and it would be too hasty to make any generalization from com- 
paratively few observations. The. present account simply deals 
with the observations upon Osmunda cinnamomea. 
Summary 
1. The reticulum in the young nucleus arises fron the chromo- 
somes of the previous division by vacuolation. It consists chiefly 
of chromatin material. 
2. The chromatin network during the resting stage shows no 
indication of a pairing of knots or strands. 
3. Individuality of the chromosomes is retained in the vacuolate 
and reticulate form during the resting stage, although the limits 
of individual chromosomes become hard to trace. 
4. The pairing of chromatin material, perhaps of maternal and 
paternal derivation, appears only at the early prophase of heterotypic 
mitosis. The pairs may come into the closest association during 
synapsis, but the duality is maintained. As a consequence no actual 
fusion occurs. 
5. There is no splitting of chromosomes in the heterotypic mitosis; 
each bivalent chromosome is formed by the association of two inde- 
pendent chromosomes. The separation of the two gives an appear- 
- ance of longitudinal division. 
THE UNIVERSITY OF CHICAGO 
