410 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
Summary 
1. The nucleus passes through a definite resting period of considerable 
length, previous to entering upon the heterotypic prophase. During this 
period all signs of the individual chromosomes are lost. The threads are 
unpaired. 
2. The approach of prophase is indicated by occasional, though not 
very striking, parallelisms in the network, due to the contraction of threads 
here and there. There is no general pairing of threads such as has been 
described by many workers on other forms. 
3. Prophase is ushered in by a general contraction of the reticulum, 
which soon causes the threads to be torn away from most of the periphery 
and to shrink into a tight knot — the synizetic knot. 
4. During synizesis, many of the threads disappear and their contents 
pass into other threads, which thus become more and more prominent, 
and finally emerge from the knot as the spireme. There is very little 
parallelism of threads during synizesis, and what little there is seems to 
be due merely to the way in which the threads condense. There is no 
reason for believing that it represents the fusion of the separated halves 
of a univalent spireme, or the synapsis of two univalent spiremes to form 
a bivalent one. 
5. There is a well marked " open-spireme " stage, during which the 
threads are fairly uniform in diameter and display no evidence of double- 
ness. There is no strepsinema condition, the nucleus passing into the 
second contraction by the gradual accumulation of material in the center 
of the nucleus, and by the contraction of the spireme thread into smaller 
and smaller loops radiating from the center, the threads composing these 
loops being single in nature. 
6. The loops can be traced uninterruptedly through the second con- 
traction, and undoubtedly form the bivalent chromosomes which emerge 
at the end of this period. The univalent chromosomes are arranged end 
to end, or telosynaptically, in these loops, the places where they join being 
marked by constrictions. 
7. The bivalent chromosomes emerge in a definite way from the second 
contraction, and are arranged in such a manner that they form one closed 
circle, consisting of four univalent chromosomes, and five rings composed 
each of two chromosomes, all of which are linked together at first according 
to a definite scheme. Homologous chromosomes are perfectly compatible. 
8. During diakinesis, these rings separate to a greater or less extent 
from one another. Each individual ring, however, including the circle of 
four chromosomes, remains intact. 
9. The rings are drawn to the equatorial plate at metaphase. The 
circle of four chromosomes breaks into two pairs. The rings are arranged 
in a fiat plate, and the univalent chromosomes are separated and carried 
to opposite poles without the least sign of irregularity. 
