The Botany of Iceland - 01.12.1928, Page 78

The Botany of Iceland - 01.12.1928, Page 78
402 JOHS. BOYE PETERSEN these forms, among which transitional forms may no doubt be found, and the nature of which is on the whole doubtful (cf. Introduction). In the Icelandic material I myself have found the forms given below. If in addition the dimensions were considered, a great many more forms might be set up. I have, however, contined myself to the following which I name pro- visionally. 1. f. typica (A. Schm. Atl. Taf. 45, fig. 19, 20). The valve linear, with rounded or less frequentljr somewhat ílattened apices. Shows considerable variation in size. 2. f. Sclimidtii (A. Schm. Atl. Taf. 45,flg. l(i). The valve linear, with more or less rostrate- truncate apices. The valve often slightly con- stricted in the middle. This form approaches P. lata v. Rabenhorstii. 3. f. subcapitata n. f. The valve narrowly lanceolate, with rostrate-subcapitate apices. Fig. 23 a. 4. f. ovalis. The valve oval in outline, about twice as long as broad. Fig. 23 b. 5. f. lanceolala. The valve rhombic-lan- ceoiate, 3 times as long as broad. Fig. 23 c. F. lypica is much the commonest of these forms. It occurred in nearly all the samples cited. F. Schmidtii occurred in samples 8, 182, 218, 254. F. subcapitata is the commonest form in Iceland after f. typica, and forms intermediate between them are often found. It occurred in samples 14, 41, 69, 121, 129, 135, 160, 161, 182, 196, 217, 307. F. ovalis is perhaps merely abnormal. A few specimens of it were found in samples 268 and 121. F. lanceolata is likewise infrequent. It occurred in samples 138. 185, 295. Fig. 23. Pinnularin borealis Ehrb. a. f. subcapilata n. f. b. - ovalis — c. - lanceolata — P. borealis has from olden times been recognised as an aérial spe- cies and is probably spread practically all over the globe. Being so common, it Will always be present in small quantitjr in fresh water samples (0strup found it in 195 samples from Iceland, but never in great number). It has been found on red snow in Antarctica (Fritsch 1912, p. 321) and on the inland ice of Greenland (Boye Petersen 1924 II, p. 315), further in numerous localities in arctic, antarctic, tempe- rate, and tropical countries. It will be easily understood that its valves are common in the atmospheric dust. (0strup 1893, p. 140). This species may therefore correctly be termed ubiquist. As regards its occurrence in Iceland I may state that it was found in the greatest quantity in samples that did not contain much manure, I have, however, found it in almost every kind of locality. That it withstands desiccation well will appear partly from Brist.ol’s (1920, p. 42), partly from my own investigations (Boye Petersen 1915, p. 24), and partly from mjr observations in Nature which would seem to show that it majr live in Iceland even on the driest ground.
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