A NOTE ON THE REVERSIBILITY OF THE WATER 

 REACTION IN A DESERT LIVERWORT 



W. A. CANNON 

 The Desert Laboratory, Tucson, Arizona 



The longer lived plants native to southern Arizona are exposed 

 each year to great variations in the water relation. The responses 

 on the part of the plants, although extremely varied, are, however, 

 so sharp as to permit the classification of the plants on this as a 

 basis. We have, thus, (1) species with a reversible water relation 

 and succulent, 1' (2) species with a reversible water relation and 

 not succulent, and (3) species with an irreversible water relation 

 and spinose or sclerophyllous. The first class is represented in 

 southern Arizona by the cacti, and the last class by the woody 

 plants in general, while the second group consists mainl}^, or wholly, 

 of certain mosses, ferns and liverworts. The last are the so-called 

 '' resurrection" plants, which become dormant on drying and 

 which revive on being moistened. It is proposed in the present 

 note to add another species to the last class, and, especially, to 

 present in a quantitative manner the amount of* water lost, when 

 the form becomes dormant, and, the amount regained, when it 

 revives. 



The observation by others on species from the more moist, 

 as well as from semi-arid regions, indicate that a fairly large 

 number have to a greater or less degree a reversible water relation, 

 as defined in the preceding paragraph. For instance, Schroder- 

 found that Corsinia marchantioides revived after having been 

 kept in an herbarium seven months, and Gymnostorium rupestre 

 and Dicranum longirostre were not killed after having been kept 

 two years in an herbarium. Pfeffer^ states that all turgid plants 



'■ The water-balance of succulent plants. D. T. MacDougal and E. S. Spaulding. 

 Carnegie Institution of Washington, Publication No. 141, 1910. 



-Quoted in Goebel's Pflanzenbiologische Schilderungen, 1 Ft., 174. 

 ^ Physiology of plants. Eng. tr., 2: 250. 



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