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PROGENY OF TRIPLOID BETULA VERRUCOSA ERH.
287
Table 2. Chromosome numbers and vitality of the progeny 44—),
triploid X triploid B. verrucosa.
Chromosome numbers
Heights of plants–-
29 30 .11 32 33 34 35 36 37 38 39 40
0—9 cm ......... 5 8 9 8 11 9 2 5 1
10—72 cm......... 2 3 2 2 1 3 3 2 1 1 2 1
dead .............. 1 2
, Totals............... 2 8 10 11 10 16 14 4 6 2 2
I o/o of totals ...... 1.90 7.(52 9.52 10.48; 9.52 15.24 13.33 3.81 5.71 3.81 1.90 1.90
| Calculated
frequencies ............ 0.00 0.00 0.00 0.01 0.04 0.14 0.45 1.16 2.58 4.89 8.00 11.33
(Chromosome numbers
Heights of plants–––––
41 42 43 44 45 46 47 48 49 50 51 Total
0—9 cm ......... 2 3 1 67
10—72 cm......... 2 2 1 1 1 1 1 1 33
de ad .............. 0
Totals.............. 4 2 0 1 1 3 0 1 2 1 1 105
% of totals ...... 3.81 1.90 — 0.95 0.95 2.86 0.95 1.90 0.95 0.95 99.96
Calculated
frequencies ............ 13.94 14.94 13.94 11.33 8.00 4.89 2.58 1.16 0.45 0.14 0.04 100.01
The results of the chromosome-niimber deterniinations are
pre-senled in Table 2. From these it is seen that plants have appeared with
all 2n numbers behveen 29 and 51 except 43 and 47. lf the 14 odd
chromosomes are assumed to be distributed at random during meiosis,
and no allowance is made for anv selective elimination of chromosome
numbers whether of gametes or zvgotes, plants with different 2n
numbers would liave appeared in the frequencies given as »calculated» in
the table. A comparison of the frequencies observed with those expected
shows a verv strong over-representation for 2n = 29—37,
under-representation for 2n = 38— 47, and a surplus, again, for 2/1=48—51. In all
probability these conditions have been brought about Ity a powerful
selective elimination of gametes and zvgotes, chromosome numbers in
the vicinity of 2n = 2x and 2/i = 4.r being favoured in lliis process.
Auto-Iriploid B. verrucosa then behaves in a männer characteristic of primarv
triploids (Johnsson, 1940), although tlie frequencv of aneuploids is
greater than in the majority of cases. Tlie relative number of the
aneuploids is not nearlv so high as in clearly secondary polyploid
tri-ploids, such as the aspen (Johnsson. 1940. 1942). Betula verrucosa (hus
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