NOTES AND COMMENT 



Dr. M. Rikli, of Zurich, has contributed to Fortschritte cler Natur- 

 wissenschaftlichen Forschung a paper entitled Richtlinien der Pflan- 

 zengeographie, which is at once an historical sketch of the progress of 

 Plant Geography and an estimation of its present activities. Three sub- 

 divisions of Plant Geography are recognized: the Floristic, the Ecological 

 and the Genetic. The operation of various environmental factors is 

 discussed in a general way at considerable length, and some recent forms 

 of instruments are described, particularly in actinometry. The habitat 

 is discussed and also the role of the individual species in Plant Geo- 

 graphical work. Rikli considers the chief function of Ecological Plant 

 Geography to be the study "of the relations between external and inter- 

 nal factors, which together are of first importance in determining the 

 distribution of individual species." Very timely and important is the 

 emphasis here and throughout his paper on the individual species of 

 plants. Ecological Plant Geography has now been concerned for a 

 number of years in the study of plant associations, chiefly by means of 

 observational methods, partially by means of methods which have been 

 designed to give observation greater exactness, and partly by means 

 of intensive study of environic factors. As the problems attacked by 

 Ecological Plant Geography become less general and more specifically 

 directed to the relation between the "exogene" and "endogene" fac- 

 tors of Rikli, the more will its activities be drawn away from the associ- 

 ation and toward the individual plant. Nevertheless, as Rikli points 

 out at the conclusion of his paper, Genetic Plant Geography has much to 

 contribute to the problems of environic factors and their effects. 



At the same time that Professor Weiss, in his vice-presidential address 

 before the botanical section of the British Association at Portsmouth, 

 is remarking on the untenability of the view that the xeromorphy of the 

 plants of the Carboniferous period may be due to their actually being 

 halophytes, Dr. Dachnowski is making a suggestion which is far more 

 plausible. In a paper in The American Journal of Science (July, 1911) 

 entitled The Problem of Xeromorphy in the Vegetation of the Carboni- 

 ferous Period he summarises the work by himself and others on the toxic 

 properties of bog water, and develops the view that the xerophilous 

 character of Carboniferous forms may be attributable to similar condi- 

 tions of toxicity in the substratum occupied by the plants of that epoch. 



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