5(3 BOOKS AND CURRENT LITERATURE 



The descriptions of both major and minor plant communities are given 

 with fullness, and with abbreviations indicating the relative abundance 

 of each species. An extended list of species brings together in systematic 

 order all of the plants collected and describes their distribution and 

 habital occurrence. 



To those who are unfamiliar with a region, a much more vivid appre- 

 ciation of its botanical aspects can be had from a few well-chosen illus- 

 trations than from many pages of the most carefully elaborated text. 

 The forty-six magnificent illustrations accompanying Skottsberg's later 

 paper, taken together with the text, and also the distributional map to 

 be found in his earlier paper, give an extremely satisfactory first account 

 of the plant geography of the southernmost portion of the western 

 hemisphere. — Forrest Shreve. 



The Mechanism of Tumor Growth in Crowngall. — As a result 

 of further studies on abnormal proliferation of cells in plants, Erwin 

 Smith concludes 1 that the stimuli act indirectly "by the removal of 

 various inhibitions" rather than directly on the protoplasm of the cell. 

 He also now believes that the agent causing proliferation is much 

 simpler than he formerly supposed. In his experiments, castor-bean, 

 tomato and cauliflower plants were injected with non-toxic doses of 

 ammonia and various ammonium salts, uric, malic, tartaric, acetic, 

 sulphuric, phosphoric, and hydrochloric acids, chloroform, sodium 

 bicarbonate, and other substances, and the result was active cell pro- 

 liferation strikingly like that of gall. It is suggested that these sub- 

 stances change the surface tension of the cells in the region injected, 

 thus lessening "physiological restraint" and leading to cell division. 

 Ammonia, as one of the metabolic products of bacteria, would saponify 

 the lipoids of the host cell membranes, resulting in the outward diffu- 

 sion of bacterial products from the invaded tissue and an inward move- 

 ment of food materials necessary for rapid growth. It appears there- 

 fore, to be unnecessary to attribute the abnormal growth of galls to 

 complex toxins. The paper includes a fine set of photomicrographs of 

 cell proliferations in the plants subjected to experiment. — J. G. Brown. 



1 Smith, Erwin F. The mechanism of tumor growth in crowngall. Jour. 

 Agric. Res. 5: 165. 1917. 



