Section 8 — Cytatoxonomy and Experimental Taxonomy 



The latter forms gave a much larger proportion 

 of polyploids. In the biennials it was more difficult 

 to induce polyploidy among others because — in 

 cases when the action of colchicine on the hypoco- 

 tyl was not strong enough — their second-year 

 spring growths were diploids. In addition, there of- 

 ten occurred mixoploid forms. Some of the species 

 are exceptionally resistant to the mutagenic 

 action of colchicine (e.g. M. suaveolens, M. 

 volgica, M. taurica). A 0.7 per cent solution of 

 colchicine failed to bring about changes in 

 these species. Progressive rises of the colchicine 

 concentrations up to a strength, resulting in a 

 total destruction of plants, did not induce 

 polyploidy. 



In regarding pollen viability as a criterion of 

 fertility, the induced polyploids greatly varied in 

 this respect. Some autotetraploids like M. offi- 

 cinales and M. alba yielded nearly 100 per cent 

 of viable pollen, while others like M. messanensis 

 only 10-15 per cent; M. hirsuta, M. segetalis and 

 M. italica about 50 per cent. Frequency in the 

 occurrence of quadrivalents, univalents and 

 polyvalents in meioses accounts partly for this 

 situation. 



Analyses of pollen viability in vitro show that 

 polyploidization changes the physiologic reaction 

 of pollen grains to the medium and to the optimal 

 temperature of germination. Differences between 

 species are great. 



Inducement of polyploidy failed to overcome 

 self-incompatibility in M. officinalis. 



8.9. (D). Evolution in the Genus Mentha from a Genetic 

 Viewpoint. M. J. Murray (Kalamazoo, 

 U.S.A.). 



The fertile species in the spicate-flowered 

 section of the genus are Mentha rotundifolia 

 {2n — 24), Mentha longifolia (2/7 = 24), Mentha 

 spicata {In = 48) and Mentha aquatica (2« = 

 96). The sterile species are M. spicata (In = 36), 

 M. niliaca (2n = 36), and M. piperita (2n = 72). 

 All colchicine-induced 4ns are fertile. Fi and F2 

 hybrids between the basic species are intermedi- 

 ate in appearance and do not resemble M. spicata; 

 but hybrids between M. spicata and An M. 

 rotundifolia or An M. longifolia are perfectly 

 fertile. M. spicata strains are highly variable in 

 leaf size, leaf shape, crispness of leaves and plant 

 habit. Contrary to popular belief, M. spicata 

 individuals do not invariably have a spearmint 

 odor with the ketones carvone and dihydro- 

 carvone. Some strains have the ketones menthone 

 and pulegone as also found in the species M. 

 aquatica and M. piperita (genotypes ccAA of 

 ccAa), while others have piperitone and piper- 



itenone as found in the basic species (genotype 

 ccaa). Selfed heterozygous strains (CcAa) give 

 a ratio of 12:3:1 for the 3 ketone types. M. 

 aquatica with 40 per cent menthofuran and the 

 menthone-pulegone ketones can be hybridized 

 to M. spicata (menthone-pulegone or piperitone- 

 piperitenone genotypes) to resynthesize M. pipe- 

 rita (2n = 72). These peppermint-odored hy- 

 brids are of substandard commercial quality in 

 having too low menthol, too high ester, and 

 tremendous differences in minor constitutents 

 (terpene hydrocarbons of which there are at 

 least 20). They differ greatly in plant habit, leaf 

 size, leaf shape, leaf crispness depending upon 

 the M. spicata parent used in the cross. Spear- 

 mint-odored hybrids occur in all crosses where 

 the M. spicata parent is spearmint-odored. 

 Diploid chromosome numbers 60, 72, 84 and 96 

 may occur in other peppermint-odored inter- 

 specific combinations. 



8.10. Cytological Studies in Section Molium of the 

 Genus Allium. S. E. Eid (Shatby, Egypt). 



The following results have been obtained: 

 I. A. blomfieldianum Asch. & Schweinf. has 

 In = 14 chromosomes with median (m) or 

 submedian (sm) centromeres. 

 II. A. neapolitanum Cir. shows two forms, an 

 allotriploid with 2n = 21 m and sm chro- 

 mosomes, and an allotetraploid with 2n = 

 28 m and sm chromosomes. The triploid 

 shows nonpairing of one set of seven chro- 

 mosomes and is sterile. 



III. A. erdelli Zucc. (including its v. roseum 

 Boiss.) has 2n = 16 m and sm chromosome 1 , 

 with four telocentrics. 



IV. A. roseum v. tourneuxiii Boiss. shows two 

 cytological forms, a diploid with 2n = 16 m 

 and sm chromosomes with two telocentrics; 

 and an autotriploid with 2n == 24 m and sm 

 chromosomes with three telocentrics. A. 

 roseum v. bulbilliferum Vis. is found to be 

 an allopentaploid with 2n = 40 m and sm 

 chromosomes with five telocentrics. It is 

 sterile and viviparous. 



The basic number in the present species is 

 shown to be seven, with centric breakage of 

 metacentrics into telocentrics in A. erdelli and 

 A. roseum. 



8.11. Species Relationship in the Genus Avena. J. H. 



W. Holden (Durham, Great Britain). 



The diploid species Avena longiglumis shows 



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