375 
and of other related Primula Hybrids. 
the greater number show 17 bivalent chromosomes together with 1 quadri- 
valent chromosome, a few show 16 bivalent and 1 quadrivalent, and one case 
was found of 15 bivalent and 2 quadrivalent. Some of the discrepancies 
may be accounted for by the fact that the nuclei appeared in two sections 
and had to be pieced together, but the trend of the results seem to prove 
conclusively that the large chromosome represents the joining together of 
two bivalent chromosomes, and this statement is further corroborated by 
the subsequent behaviour of the large chromosome on the equatorial plate. 
It is interesting to note that Rosenberg ( 33 ) in the hybrid Drosera 
obovata found that the chromosomes in the homotype division sometimes 
appeared as tetrads, and remarks ‘ dass wir in dem Vorkommen der Vierer- 
gruppen im zweiten Teilungsschritt einen Ausdruck der Hybriditat sehen 
konnen ’ (p. 116). 
Strasburger ( 35 ) in Melandriitm rubrum describes one chromosome in 
the heterotype division which is much larger than the others ; it reappears 
in the homotype division, and is present also in the embryo-sac mother-cell. 
Agar (1) noted a conspicuously larger pair of chromosomes in Lepido * 
siren paradoxa , which are seen in the spermatogonial divisions, and which 
can be identified throughout the two maturation divisions. 
In both Melandrium and Lepidosiren the large bivalent chromosome 
results from the association of two proportionately larger univalent chromo- 
somes, and not from the temporary union of two bivalent chromosomes as 
in P. kewensis (fertile). 
The spindle of P. kewensis (fertile), like that of the other Primulas, is 
quadripolar at its origin (Fig. 93). When the chromosomes have completed 
their equatorial arrangement, the quadrivalent chromosome is easily re- 
cognized (Figs. 94 and 95). Sometimes before the other chromosomes have 
separated, the quadrivalent chromosome may have prematurely divided 
into its four univalent units, though the members of each pair may continue 
to be joined one to the other (Fig. 94) ; in other cases the quadrivalent 
chromosome may not divide until the other chromosomes are about to pass 
to the poles (Fig. 95). The chromosomes have been counted several times 
in the polar views of equatorial plates. In several cases the number has been 
found to be 18 (Fig. 96), but 17, 16, 15, and even 14 chromosomes have been 
counted. Possibly this inaccuracy may be due to the position and relative 
degree of separation of the quadrivalent chromosome. This suggestion 
is supported by the fact that polar views of anaphases and polar views 
of asters (PL XLIV, Fig. 99) almost invariably show 18 chromosomes. 
As they proceed to the poles (PL XLIII, Fig. 97) the univalent chromo- 
somes which composed the quadrivalent combination cannot be distinguished 
from the others (PL XLIV, Fig. 98). The anaphase and telophase have been 
studied in detail, and there is no reappearance of the large chromosome. 
The chromosomes of the late anaphase at first mass together (Fig. 100), then 
C c 2 
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