Pollen Development in Lachica . 389 
chiasmatypy can only be harmonized with the conclusions of other observers 
regarding the formation of rings by assuming k that the chiasmatypy has 
taken place during a strepsinema stage prior to the straight, longitudinally 
divided threads from which the rings arise’. He further says (p. 208 ): 
4 No observer, so far as I know, has yet seen a process of true crossing-over 
(recombination) by means of torsion, chiasma formation, and secondary 
splitting apart . 5 The torsion described in this paper as occurring during 
and after the looped stage of the pachynema if followed by breaking across 
the segments and crossing-over, as appears clearly to be the case in some 
instances, furnishes exactly the type of redistribution called for, but is 
obviously quite a different thing from the -chiasmatypy of Janssens. This 
type of twisting is common enough in plant chromosomes during this 
period. The absence of evidence of such a process in animal chromosomes 
leads Wilson to suggest that the crossing-over phenomena may find their 
basis in some process of torsion during or after synapsis. He even suggests 
some ‘ internal process of torsion 5 or rotation* in the early pachytene stage 
before the duality of the diplotene thread becomes externally visible. The 
clear evidence of torsion in plant chromosomes makes it probable that 
a similar basis for crossing-over will be found in animals where the 
phenomenon has been analysed genetically on a large scale. 
Chromosome Fusions. 
Examination of the literature discloses a considerable number of cases 
of temporary fusions of various kinds between the chromosomes, both in 
plants and animals. One of the first cases of a partial or temporary 
connexion between chromosomes was described by Nawaschin (1912) in 
root tips of Galtonia. Several investigators have shown that in Galtonia 
there are eight pairs of chromosomes of varying lengths. Two of those 
pairs are very small and lie centrally in the chromosome group. Nawaschin 
calls them satellites. He finds that in prophase they lie on the surface of 
the nucleolus. Digby (1910) showed that in anaphase they pass to the 
poles in advance of the other chromosomes. Nawaschin found one pair 
constantly attached to the inner end of a certain pair of long chromosomes. 
Tschernoyarow (1914) has found in Najas major , in agreement with Muller 
(1912), seven pairs of chromosomes which are morphologically distinguish- 
able, one pair being very small. In the heterotypic metaphase Tscherno- 
yarow finds only six pairs of chromosomes, owing to the fusion of these 
satellites with one of the long pairs. This attachment was also observed 
in prophase. In this way the discrepancy between Guignard (1899), who 
counted twelve chromosomes in the reduction divisions, and Muller (1912), 
who counted fourteen in somatic mitoses, is explained. This type of 
temporary fusion appears to be similar to the one described in Lactuca. 
It differs, however, in the greater uniformity of its occurrence and in the 
