Studies on Asynapsis in the Elm, Ulmus Glabra Huds

HE occurrence of asynapsis (i.e. decreased chromosome pairing T at first metaphase) has been reported in several plant species since 1927, when LESLEY and FROST published their investigation of Matthiola incuna.In 1943 a survey of species known up to that time was given by PRAKKEN.Since then further cases have been discovered, e .g ., in Rirmex (LUVE, 1943), Musa (DODDS, 1943), Alopecurus myosuroides (JOHNSSON, 1944), Triticuin (Lr, PAO and LI, 19451, Phleum ( NORDENSKIULD, 1945), Triton ( BUUK, 1945), and Picea ( ANDERSSON, 1947).The present case, asynapsis in Ulmus, was discovered in 1943, further researches being conducted in 1944 and 1947 at the Forest Tree Breeding Institute, Ekebo, Kallstorp, Sweden. Maferial and methods.-Three asynaptic elins (NOS. 1, 7 and 10) from KlirrbogHrde, VHstergctland, and nine normal ones (Nos.2, 3, 4, 8, 9, 11, 12, 13 and 14) growing at the same place webe included in the investigation.One more normal elm from Fjarrestad, Sklne, was used in the crossing experiments.The morphology of tree No. 1 differed slightly fr'om that of normal elms, the leaves being somewhat broader and darker, the branches thicker and thie buds bigger; but lhese characteristics, indicating polyploidy, were probably due to environmental influences, since the chromosome number, dletermined in vegetative cells in the buds, was that characteristic of Ulmus glubra, i. e. 2n = 28, and the mean length of the stomata did not differ from that of normal elms.The origin of the Karrbogarde trees is not known, but most probably they are of the samle provenience as the other wild-growing elms in this district.Branches were taken from the elms between December and February, Porced in water culture in a greenhouse for 3 to 6 days, after which the buds were ready for fixation.Chrome-acetic-formalin was used as fixation Iluid after prefixation with Carnoy.Staining was carried out with gentian violet, or in some cases with Feulgen.In both cases good results were obtained.Heredltas XXXV. 1 2 CARIN EKLUNDH EHRENBERG 5 Figs.1-3.Somatic mctaphasc plates of Ulmus glabra.-1.diploid (2n = 288).-2.triploid (2n = 42).-3.tetraploid (2n = 56).-Figs.4-7.Elm No. 2, iiortnal.Meiosis in PMC's.-4.diplotene pairs, separately drawn.-5.early diakinesis, 1411.-6.I-M (all bivalcnts not visible).-7.II-M.To allow of the use of these asynaptic elms in crossing experiments other branches were grafted on 2-3 years elm plants, inserted in pots.The method used here -))bottle grafting,, described in detail by JENSEN (1942) and by JOHNSON (1945)is generally employed at the Forwt Tree Breeding Institute at Eltebo, SliAne, when working with species which have a specially short seed ripening time.The graftings and crossings were carried out in the greenhouse at the end of February, 1944, the seeds being sown immediately on maturing about a month later.Root tips of the young cross plants were fixed in chrome-aceticfornialin in the course of July-August; then cut into 14 ,u sections and stained with gentian violet.The pollen was stained with aceto-carmine.In measuring the diameters of pollen grains and the stomata lsengths, a 40 X objective and a 15 X ocular were used, one unit of the scale equalling 2,4 ,u, The statistical analysis was performed according to BONNIER and TEDIN (1940).