THE CYTOLOGICAL BASIS OF POLYMORPHISM IN POA ALPINA

MUNTZINGisland was visited rather early in the season and therefore living plants had to be taken, no seeds being ripe.The other island, Gotland, was visited somewhat later and in this case seed material could be obtained.Additional material from Sweden, Norway, Iceland and Greenland was obtained thanks to the courtesy of several colleagues.My sincere thanks for this valuable collaboration are due to Doctors C. L. KIELLANDER, J. A. NANNFELDT, S. ERLANDSSON, G. OSTERGREN, N. ALBERTSSON, A. L6vE, M. WESTERGAARD, C. A. J6RGENSEN, and E. RUNQUIST.During my own collecting trips Mrs. G. MUNTZING functioned as a sharp-sighted observer who discovered many biotypes which would otherwise have been overlooked.The seed material collected in North Sweden was germinated in the spring of 1943 and the full-grown plants studied in the summer of 1944.Some of the plants collected in North Sweden in 1942 produced panicles and ripe seeds in the same year after transplantation to Svalof'.Progenies of these plants were included in the material germinated in the spring of 1943.Other transplanted plants did not produce seeds until 1943, and in these cases progenies were raised in the spring of 1945.At the same time the material from Oland and Gotland was germinated as well as new progenies from the North Swedish material studied in 1944.The Gotland material was raised from panicles collected in the natural habitats, the Oland material from panicles produced at Svalof in the year of transplantation.With few exceptions the progenies were raised from seeds of a single openpollinated panicle, each progeny consisting of 16 plants or a slightly lower number, owing to mortality in the field.As a rule, root-tip fixations were made of three plants per progeny and also, before that, of all the plants collected in the field and sent to Sval6f.The root tips were fixed in diluted chrome-acetic-formalin, the plants before fixation being kept over-night at low temperature (slightly above zero) to bring about chromosome contraction which greatly facilitates the counts.The root tips were sectioned and stained with crystal violet.My sincere thanks are due to Miss.M. PALM and Miss J. \VARDEN for valuable help with the somatic chromosome counts. II. CHROMOSOMAL VARIATION.A summary of all chromosome numbers determined in the seedproducing biotypes is given in Table 1.With certain exceptions, to be discussed below, this table roughly expresses the chromosomal variation 16015223, 1954, 3-4,

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