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1917] CURRENT LITERATURE 525 



rate at the original temperature. It was found that after a change in tem- 

 perature, the corresponding change in respiratory activity took place only 

 gradually, apparently not having reached an equilibrium even at the end of 

 the third 20-minute period. Although the main point is proved, the value of 

 this part of the work would have been increased by continuing the observations 

 over a longer time. 



Many students will regret that the author did not study oxygen consump- 

 tion as well as the production of C0 2 , to see whether the respiratory coefficient 

 was altered by temperature changes. It should be remembered, too, that the 

 conclusions reached may not hold good for other sorts of material, such as 

 dormant seeds, the germination of which is greatly stimulated by alternations 

 of temperature. — G. T. Harrington. 



Ecology of bryophytes and lichens. — Ecological studies of liverworts and 

 c mosses have not been numerous in the past, largely because bryologists have not 



been interested in ecology and ecologists have not been sufficiently acquainted 

 with bryophytes. There are also some difficulties peculiar to the application 

 of ecological principles to these plants. Some of these have been pointed out 

 by Watson 4 in attempting, among other things, to define a xerophytic bryo- 

 phyte. This he decides must be a plant capable of withstanding long periods 

 of dryness and of having at the end of such periods sufficient living cells to 

 enable it to resume its growth quickly when water becomes available. He 

 proceeds to consider the " xerophytic adaptations" under the two principal 

 heads of structures causing (1) reduction of water output and those resulting 

 in (2) water storage. The former is accomplished by such means as cushion 

 forms, investments of dead cells, thick cell walls, leaf arrangement, and capillary 

 structures; the latter by water sacs, water-storing cells, mucilaginous cells, 

 and succulent tissue. The writer, however, warns us that many bryophytes 

 exhibiting " xerophytic adaptations" are not xerophytes. 



A second paper by the same author 5 gives in detail the zonation of bryo- 

 phytes in a wet heath. The shallow water zone is dominated by Aneura 

 pinguis, P cilia epiphylla, Hypnum scorpioides, and Sphagnum cymbifolium; 

 the second zone, just above water level, is dominated by Aneura midtifida; 

 a third zone consists of Sphagnum subnitens, Hypnum intermedium, and asso- 

 ciated forms, passing imperceptibly into a fourth zone, characterized by Hypnum 

 cuspidatum, and closely followed by a fifth zone dominated by Brachythecium 

 pyrum and Cephalozia connivens. This is frequently the end of the series, 

 although occasionally the drier tussocks show a sixth zone of Hypnum cupressi- 

 forme var. ericetorum. Drainage and the accumulation of humus are the chief 



4 Watson, W., Xerophytic adaptations of bryophytes in relation to habitat. 

 New Phytol. 13:149-169, 181-190. 1914. 



s % A Somerset heath and its bryophytic zonation. New Phytol. 14:80- 



93- 1915- 



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