158 Digby. — On the Archesporial and 
(seedling), second contraction is omitted, so that the sequence of phases 
extending from the first indication of the conjunction of univalents (fila- 
ments) to the realization of the mature bivalent chromosomes can be traced 
without intermittence. In Osmund a the conjunction of filaments in late 
hollow spireme is conspicuous in well-fixed preparations, but the fact that 
fission may persist nearly to second contraction adds a perplexing feature. 
In Galtonia there is no convincing evidence for conjunction, but as the 
nucleus approaches second contraction the univalents (filaments) tend to 
conjoin in pairs to form bivalent segments. In Crepis virens, notwithstand- 
ing that the haploid number of chromosomes is but 3, it is impossible to 
trace their evolution, owing to the viscous character of the nuclear contents, 
and also to the fact that the hollow spireme stage is usually omitted, the 
nucleus passing almost directly from synapsis into second contraction. 
From the foregoing remarks it will be realized that no one of these 
four plants is completely satisfactory throughout its phases, but if the 
telophases of the last premeiotic division and the early heterotype prophases 
of Galtonia could be combined with the later presynaptic and synaptic 
phases of Osmunda , and the hollow spireme to diakinesis stages of Primula , 
a completely coherent and intelligible series of nuclear phases would be 
established. 
3. The Evidence afforded by Osmunda. 
The conclusions of several investigators with regard to the origin of 
the heterotype chromosomes in Osmunda are somewhat at variance. 
In 1900 Strasburger ( 17 ) incorporated a short account of the hetero- 
type division of O. regalis in a paper dealing with a variety of subjects. 
He does not inquire into the manner in which the chromosomes are reduced, 
as he assumes the heterotype prophase to be predestined to evolve the 
x number. The fission which appears in the spireme, soon after it has 
emerged from synapsis, he regards as the premature splitting apart of the 
two univalent chromosomes which will separate on the equatorial plate of the 
heterotype spindle. Great emphasis is laid on the fact that this separation 
is immediately followed by a second longitudinal fission for the homotype 
division. 
Farmer and Moore (8) in 1905 showed that a similarity in the process 
of reduction occurs in animals and plants, and O. regalis was one of the 
plants selected. They describe the close conjoining of the sides of the 
loops at the onset of second contraction, each side eventually forming 
a univalent segment of the heterotype or bivalent chromosome. Further, 
that * the homotype mitosis is associated with the completion of the longi- 
tudinal, division of the chromosomes already incepted during the prophase of 
the heterotype division ' (p. 505). 
In 1907 Gregoire (10) cited Osmunda as strongly supporting the para- 
synaptic theory, and in this paper appears his historical figure of a nucleus 
