1920] CURRENT LITERATURE 351 



throw, resulting in a talus or fan on the lee side, (2) by percolation, especially 

 where there is large tidal difference, or (3) by stream scour on the lee side. 

 Suaeda fruticosa is able to colonize upward growing shingle, quite as Psamtna 

 may colonize an upward growing dune; Suaeda is an especially good pioneer, 

 because of its halophytic proclivities. Later stages, as shingle growth 

 decreases, are characterized by mat plants such as Silene maritima and Con- 

 volvulus Soldanella. A plant of the latter increased' in area within four years 

 from 9 to 525 square feet. 



An interesting chapter deals with the reclamation of salt marshes. It 

 is Oliver's view that a marsh would not fill alone by silting, by reason of alter- 

 nate filling and cutting. Reclamation may be brought about naturally by 

 coastal elevation or by the building up of a barrier dune, or it may be brought 

 about by artificial agencies. A remarkably effective plant reclaimer of halo- 

 phytic shores is Spartina Townsendii, a supposed natural hybrid of S. stricia. 

 and S. alternifiora. This species was first noted at Southampton in 1870, and 

 now covers thousands of acres. In 1895 it appeared at Bayonne, on the 

 Bay of Biscay. It is interesting to note that these two areas are the 

 only ones known where the areas of the supposed parent species overlap. 



H. C. Cowles. 



NOTES FOR STUDENTS 



Root systems. — Since the notable work of Cannon in 191 1 on the roots of 

 desert plants, nothing has contributed so much to our knowledge of subter- 

 ranean plant organs as the recent publication by Weaver, 2 in which he has 

 described the root systems of some 140 species of shrubs and herbs from the 

 prairies of Nebraska and Washington, the plains and sand hills of Colorado, 

 and some gravel slide and forest communities of the Rocky Mountains of 

 Colorado. For each of the habitats under investigation many data regarding 

 such environmental conditions as rainfall, evaporation, and soil moisture are 

 given. These data and the abundance of illustrative drawings and photo- 

 graphs of excavated root systems are among the most valuable features of the 

 report. 



In the Nebraska prairie there is a striking individuality in the root sys- 

 tems, and a grouping of the roots into more or less definite absorbing layers, 

 thus reducing competition and permitting the growth of a larger number of 

 species. The deeper rooted species comprise 55 per cent of the 33 species 

 examined, and extend beyond a depth of 5 feet, some reaching as much as 

 20 feet below the surface, many of them having few or no absorbing roots in 

 the first few feet of soil. The majority of the deeply rooted species are dicoty- 

 ledons; but it is notable that the group also includes three dominant grasses, 

 Panicum virgalum, Andropogon furcatus, and Agropyron repens. In contrast 



2 Weaver, J. E., The ecological relations of roots. Carnegie Inst. Wash. Publ. 

 286. pp. vii+128. ph. 33. figs. 58. 1919. 



