45 2 Gregory .-Spore-Formation in Leptosporangiate Ferns . 
chromosomes, which, I think, must be looked upon as independent of the 
transference of stainable matter from or to the nucleolus. 
Cannon has suggested a ‘ cytological basis for the Mendelian laws 1 ’ 
founded upon the occurrence of a qualitative reduction-division, and pre- 
dicted the discovery of a qualitative reduction in plants. A similar sugges- 
tion was independently made by Sutton 2 . 
Cannon’s hypothesis consisted in the assumption that in fertile hybrids, 
as well as in pure races, ■ the chromosomes derived from the father and the 
mother unite in synapsis, and separate in the metaphase of one of the 
maturation divisions ... so that the end is attained that the chromatin 
is distributed in such a way that two of the cells receive pure paternal, and 
two cells pure maternal chromosomes, and no cells receive chromosomes 
from both the father and the mother.’ 
Thus enunciated the hypothesis is applicable only to monohybrids 
(de Vries) ; it is insufficient to explain the phenomena observed in the 
offspring of Mendelian hybrids whose parent-races differ from one another 
in respect of more than one pair of allelomorphic characters. 
This was recognized by Sutton, who therefore paid particular attention 
to the positions assumed by the chromosomes in Brachystola. He says : 
‘ The results gave no evidence in favour of the parental purity of the 
gametic chromatin as a whole. On the contrary, many points were dis- 
covered which strongly indicate that the position of the bivalent chromo- 
somes in the equatorial plate of the reducing division is purely a matter 
of chance, that is, that any chromosome pair may be with maternal or 
paternal chromatid indifferently towards either pole, irrespective of the 
positions of the other pairs, and hence that a large number of different 
combinations of maternal and paternal chromosomes are possible in the 
mature germ-products of an individual.’ 
Hacker 3 and Ruckert 4 have shown that in Cyclops , as in A scar is and 
other forms 3 , the germ-nuclei do not fuse completely in fertilization, but 
give rise to two groups of chromosomes, which lie side by side in the 
succeeding mitoses. Hacker 5 has since traced the autonomy of the 
paternal and maternal chromatin in Cyclops from fertilization up to 
the formation of the mother-cells of the gametes. 
In the primary oocyte the twelve tetrads are arranged in two groups, 
each consisting of six tetrads, which occupy parallel planes across the 
‘ provisorische Teilungsfigur.’ 
At a later stage the two groups are separated by a partition-wall, 
which extends across the nucleus, and Hacker suggests that those of the 
tetrads which lie upon one side of this wall are of paternal, those upon 
the other side of maternal origin. In the ‘ secundaren Keimblaschen ’ the 
1 Cannon, ’02. 2 Sutton, ’03. 3 Hacker, ’92. 
4 Ruckert, ’95. 5 Hacker, ’03. 
