28 BOTANICAL GAZETTE [july 



Banksiana, nor any cottonwood dunes similar to those of the 

 Indiana-Michigan region. There are practically no panne colonies, 

 but a few isolated oval groups, chiefly of Thuja and Betula alba, 

 which seem to have originated from pannes, growing upward as the 

 sand accumulates around their stems. A few other patches have 

 reached the low conifer stage, but seem chiefly to have been inva- 

 sions from the relic patches previously described. On the open 

 sand the vegetation consists of characteristic pioneer herbs, Am- 

 mo phila and Calamovilfa among grasses, with Lathyrus maritima, 

 Artemisia caudata, Campanula rotundifolia, Cirsiiim Pitcheri, some 

 Hudsonia, and Zygadenus chloranthus. There are frequent mounds 

 protected by Calamovilfa, Prunus pumila, Salix syrticola, and 

 Cornus stolonifera. 



The growth of grasses, especially Ammophila, is quite extensive, 

 and frequently approaches the character of fixed grass dunes. This 

 is especially noticeable on the advancing lee slopes, where the com- 

 plex is overwhelming the climax forest. 



Literature 



In view of the state of our knowledge of the general subject, the 

 literature was reviewed rather fully, but only a brief summary of the 

 results will be given here. The survey covered only the extension 

 and distribution of soil roots, and the questions of absorption, 

 structure, and effects of environmental factors were considered only 

 as they affected extension. Owing to the range of the subject, the 

 matter was treated from the standpoint of lines of work followed 

 rather than that of historical development. These will be sum- 

 marized and general conclusions indicated. 



Intensive study of root systems. — This line has been fol- 

 lowed mostly by German workers, and was directed chiefly toward 

 the questions of structure and function, either in different roots of 

 the same maturity or in the same root at different stages of its 

 development. The leading workers along this line were vox 

 Alten (i), Freidenfeldt (i6, 17), and Tschirch (43). Kroemer 

 (24) has made the most thorough study of the ''biological" sig- 

 nificance of structure, and concludes (i) that the root is divided 

 longitudinally into zones characterized by greater or less suberiza- 



