-67- 



REVIEW— A RECENT CONTRIBUTION TO THE ECOLOGY OF MOSSES 



L. W. Riddle 



The Bryophytes are of special interest to the student of plant evolution 

 as being the first group to adopt the land habit. This change from the aquatic 

 habit of the ancestral algae to the land habit of the bryophytes may be looked 

 upon as one of the most critical changes of environment taking place during the- 

 evolution of the plant kingdom. It meant, first of all, that the plants must 

 solve the problem of living without a continuous supply of free water, and^ 

 furthermore, of resisting, at least in a dormant condition, the periods of drouth 

 which must necessarily occur. As we should expect, the liverworts, with the- 

 exception of certain of the higher genera such as Frullania, have advanced a 

 comparatively short distance in the solution of the problem, being mostly still 

 confined to wet habitats. But when we come to the mosses, we find a group 

 distributed over a diversity of habitats, and living successfully even under such 

 severely adverse conditions as exist on tree trunks and on rocks, where they are 

 exposed to the drouths of summer and to the freezing temperatures of winter. 

 Any contribution to our knowledge of the ability of mosses to withstand these 

 conditions is welcome. 



We, therefore, turn with interest to a recent paper by Irmscher, "On the 

 Resistance of Mosses to Drying and to Cold"^ containing the results of an 

 investigation carried on at Leipzig, in the laboratory of Professor Pfeffer, our 

 foremost authority on plant physiology. The paper contains twenty-seven 

 tables giving the statistical results of experiments on a variety of mosses, with a 

 discussion of the data thus obtained and a series of conclusions. In order to 

 give the results of Irmscher's investigations to the readers of the Bryologist, 

 a translation of the more important of the conclusions is here given, -together 

 with some of the data upon which these conclusions are based. 



1. Mosses possess in general a great resistance to continuous desiccation 

 by evaporation of the cell sap. Thus, even a moss of wet habitats, such as 

 Hypnum aduncum, required 28 weeks of drying before all of the leaf cells were 

 killed. 



2. This resistance, however, varies distinctly according to the habitat to- 

 which the particular species has become adapted. This may be illustrated by 

 a. comparison of the length of time required to kill the leaf cells of mosses grow- 

 ing on soil and of those growing on rocks and trees. 



On soil: On rocks and trees: 



Mnium rostratum 8 weeks Ulota Ludwigii 50 weeks 



Funaria hygrometrica 13 weeks Orthotrichum speciosum. . .60 weeks 



.Catharinea undulata 25 weeks Rhacomitrium canescens. . . 60 weeks 



While the remarkable fact appears that after 128 weeks (nearly two and one 



^ Edgar Irmscher. Ueber die Resistenz der Laubmoose gegen Austrocknung und Kalte^ 

 Jahrbiicher fiir wissenschaftliche Botanik 50: 387-449. 1912. 



