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28(5 HELGE JOHNSSON
Table 1. Fertility of triploid b. verrucosa.
Cross No Number of fruits "/ii fruits with embryo Number of plasts
ob-tained
with embryo without ein bryo
44—1 Triploid, Vänjan X Triploid, Kode .................. 481 3.381 12.45 140
44—4 Triploid, Kode X Triploid, Vanjan .................. 15 794 1.85 4
Total for Triploid X Triploid ........................ 496 4.175 7.15 144
44—3 Triploid, Vänjan X B. pubescens..................... 5 988 0.50 4
44—5 B. pubescens X Triploid, Vänjan.................... (1 2.668 0.00 —
Total Triploid X B. pubescens and reeiprocal . 5 3.656 0.25 4
45—15 Triploid, Vänjan X B. verrucosa A................ 3 233 1.27
45 — 16 Triploid, Vänjan X B. verrucosa B................ 177 635 21.80 —
Total Triploid V B. verrucosa ........................ 180 868 11.54 —
44—2 Triploid, Vänjan y&B. (ptibescensX verrucosa) ... 0 306 0.00 .—
to be decidedly lower than when triploid B. verrucosa is mated with
forms of the same species. Between the two species B. verrucosa and
B. pubescens there is also a strong sterilitv barrier (.Johnsson. 1945).
Triploid B. verrucosa^triploid (B. pubescensXverritcosa) has not
yielded anv matlire seed. Frnits with embryos are germinable in
varietv crosses up to practicallv speaking 100 °/o. However, from the
triploid cross, which has given llie greatest number of fruits with
embryos, 481, the yield has been only 140 plants that have been
suffi-ciently vital to survive the first summer. In spite of this. almost all
embryos developed a little after the sowing, thougli a large number died
at different stages of their earliest development.
The chromosome number of the triploid progenies is naturally of
great interest, especially in view of the practical baekground of these
experiments, viz. the raising of tetraploid individuals for breeding
purposes. It has not been possible to follow the meiosis of the triploids
in detail, hut so much has beeome clear. that it is highlv irregulär
with numerous trivalents and Univalents (Johnsson. 1944). The
chromosome number of the progeny, however, is not only determined by
the course of meiosis hut also by the selection of gametes and zygotes
that mav occur. Within the progeny 44-1 the 2n numbers have been
determined for 105 of the 140 plants, while the remaining 35 plants were
too weak for fixation.
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