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present understanding of their possible history, special studies of selected groups are more likely to give us definite answers to some of the most crucial questions raised. Nevertheless, such special cases cannot easily be selected before certain general studies have been made, and so we are forced to spend considerable time to complete the general survey of the cytotaxonomy of these floras before we can concentrate on special cases. However, special groups are being selected from time to time whenever species or genera are found to be promising for detailed studies by aid of transplant and hybridization experiments.

We and other cytotaxonomists working with the arctic-alpine plants regard it as most important to get information about the chromosome number of all the species of this element as soon as possible, to secure the use of the biological species concept as a background for these general and special investigations on the history and origin of the flora as a whole. Thanks to several cytotaxonomists in many lands, much of this basic work has already been accomplished. The chromosome number is now known in more than eighty per cent of the species of the arctic and hemi-arctic zones, somewhat less in Asia, somewhat more in the Atlantic sector, and up to one hundred per cent in Iceland, which has been studied by us. The chromosome numbers of some Asiatic mountain plants have been thoroughly counted by Sokolovskaja and Strelkova, those of the plants of the Alps are being studied by Favarger and his group, and those of the plants of the Polish Tatra Mountains by Skalińska and her associates, continued under the guidance of our former associate, Pogan. Most other boreal mountain floras remain very insufficiently known. Some Japanese botanists, mainly Funabiki and our former students Kawano and Tateoka, have made pilot studies of the chromosome numbers of Japanese alpine plants, and our one-time associate, Packer, has made reasonably intensive studies of the chromosome numbers of plants from alpine situations in Alberta and Alaska. We and our associates in Montreal and Boulder have made certain introductory studies of the alpine floras of the Sierra Nevada complex in Spain, in the mountains of Gaspé, the Green Mountains of Vermont, and in the Alberta and Colorado Rockies, and completed an analysis of the cytotaxonomy of the entire flora of alpine plants on Mt. Washington in the White Mountains of New Hampshire. Contrary to some of the plants that we have already observed in the Colorado Rockies, the alpine flora of the White Mountains in the East seems to have dispersed southwards from the northlands at a relatively late date.