62 



Aug. 8. This is a plant of high northern distribution, appearing 

 also in the Alps. The identification of my specimen rests upon 

 its perfect agreement with one from northern Norway collected 

 by Hagen, without the help of which it would probably have 

 remained undetermined. As the fruit of this species is as yet 

 unknown, its generic affinities are perhaps not absolutely certain. 

 Didymodon is at best an artificial genus. 



6. Tortula suhulata (L.) Hedw. On rocks at Seydhisfjordhur, 

 July 8; on the lava-field by Hafnarfjordhur, July 23; on rocks 

 by the waterfall Trollafoss near Reykjavik, July 28. This 

 species must be common and it is probably due merely to an 

 oversight that Gronlund omitted it from his revised list of 1881 

 after having included it in his preliminary one of 1873. 



7. Pohlia polymorpha Hornsch. On lava-field by Hafnar- 

 fjordhur, July 23; on slope of Lagafell near Reykjavik, Aug. 4. 

 This species was fully to be expected and is doubtless not 

 uncommon. 



Ithaca, N. Y. 



REVIEWS 



Clements's Plant Succession "^ 



An important stage in the development of ecology is marked 

 by the appearance of Doctor Clements's Plant Succession. This 

 large and comprehensive work is the first systematic monograph 

 on the series of complex phenomena in the development of 

 vegetation called succession. It contains in addition to the 

 author's own investigations a full account of the literature not 

 only of the United States but of the entire world. 



Just as many students of modern ecology have found Research 

 Methods in Ecology (1905) so helpful in solving problems in a 

 quantitative manner, likewise the rapidly growing ranks of 

 synecologists may well turn to Plant Succession for a clear 

 statement of the development of the subject, its present status, 

 and its future outlook. Clements's work in the field for 20 



* Plant Succession, an analysis of the development of vegetation. Frederic 

 E. Clements, professor of botany in the University of Minnesota. Carnegie 

 Institution of Washington, 1916, pp. i-xiii -t- 1-512, with 61 photographic plates 

 and 51 figures in the text. 



