Polyploidy and Winter Survival in Panicum virgatum L. 1

T HE problem of polyploidy in relation to environment has received a good deal of attention during recent years. The opinion of some European workers that polyploid species, or races thereof, are better adapted to unfavorable environmental conditions has not been borne out completely by all workers. The results of the statistical study made by L6ve and L6ve (3) 3 regarding the chromosome numbers of plants from certain localities from Timbuctoo to Spitzbergen are clearly defined. These workers found a marked increase in the frequency of polyploid species as the latitude increased. This frequency also increased with a change from a temperate to a cold climatic region. They included in their summary the statement that, "It is suggested that this fact is the result not only of the relatively greater hardiness or adaptability of polyploids than diploids to more extreme climates, but also of the possibly relatively higher frequency of longday or neutral reactivity to the photoperiod within the polyploids than within the diploids". Sixty-four per cent of the 87 species examined from the Arctic island of Kolguev were found to be polyploids by Sokolovskaya and Strelkova (7). It may be questioned whether the conclusions based upon such data are entirely applicable to intra-specific chromosomal variation even though they appear clear and definite for inter-specific comparisons. Gustafsson (~) has recently discussed the possible relations and effects of glaciation upon the flora immediately before the ice sheets. He offered the suggestion that, "The diploids get destroyed because their mechanism of heterosis betrays them; in large populations crossbreeding (and its consequences) means an advantage,, in isolated remnants it implies destruction. Thus what should be compared from a viability point of view, is not the polyploid status itself contra th~ diploid, but rather the polyploid biotypes contra the isolated sum of the inbred diploids still alive". Later in the same paper he points out that, "The inferences of polyploid superiority, involving, for instance, improved cold-hardiness effected by the polyploid state itself must be taken with great caution. Pot a fair comparison every genus and every flora must be examined separately". Schwanitz (5), in his discussion concerning polyploidy and phylogeny, referred to the importance of heterozygosity as it relates to the hardiness of plants. This was considered to be an effective mechanism for selective action in the formation of genotypes tolerant to cold." Some additional data pertaining to intra-specific polyploidy and