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THE AMERICAN NATURALIST 



[Vol. L 



of course individuals which at the time of the examination had 

 not yet developed fruiting organs. More extended studies of 

 Lewis 6 have established the seasonal habits at "Woods Hole, Mass- 

 achusetts, of the above species of Polysiphonia, Griffithsia and 

 Dasya. Tetraspores and carpospores were germinated on shells 

 that were fastened to piles and left over winter. In June tetra- 

 sporic plants of carposporic origin were abundant, which, re- 

 leasing their tetraspores in July, produced a crop of sexual plants 

 that matured their carpospores in August or early September. 

 The small plants from the carpospores winter over and produce 

 the tetrasporic plants of the first summer generation. Thus the 

 sexual generation is conspicuous in the late summer while tetra- 

 sporic plants surviving the winter are characteristic of the 

 spring. Belated growth of tetrasporic plants may result in their 

 fructification late in summer, so that a few small carposporic 

 plants also winter with the tetrasporic but they are rela- 

 tively scarce. The seasonal history is then in the main char- 

 acteristic ; tetrasporic plants appear in the spring and through 

 their spores produce a summer crop of sexual plants, from the 

 carpospores of which a generation of small tetrasporic plants in 

 favorable situations carries the species through the winter. This 

 experimental work thus supports at all points the conclusions of 

 Yamanouchi based on cytological studies. 



The most important cytological work on life histories in the 

 red alga? since the paper of Yamanouchi on Polysiphonia is that 

 of Svedelius presented in studies on Martensia, Delesseria, Nito- 

 phyllum and Scinaia. Part of this work, described in the next 

 paragraph, concerns the development of tetraspores in multinu- 

 cleate tetrasporangia (Martensia and Xitophyllum). All of it 

 supports to the fullest degree Yamanouchi 's theory of alternation 

 of generations in such species as have tetrasporic plants in their 

 life histories. The work on Scinaia presents a most interesting 

 hypothesis for the life histories of such red algae as do not develop 

 tetraspores. 



The life history of Delesseria sanguinea is discussed by 

 Svedelius 7 in three papers embodying cytological work of a high 



e Lewis, I. F., "The Seasonal Life Cycle of Some Eed Algae at Woods 

 Hole," Science, XXXIX, 253, 1914. 



• Svedelius, N., "Ueber den Generationswechsel bei Delesseria sanguined," 

 Svenslc. Bot. Tidskr., V, 260-324, 1911. "Ueber die Spermatienbildung bei 

 Delesseria sanguinea," ibid., VI, 239-265, 1912. "Ueber die Zystokarpien- 

 bildung bei Delesseria sanguinea," ibid., VIII, 1-32, 1914. 



