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centrate. On the other hand, it is comparatively well known that 

 many cryptogamous plants are able to adapt themselves to the 

 presence of such concentrates, and sometimes are even favored 

 by their presence. This is particularly true among the fungi, and 

 to a lesser extent among the bryophytes. When we consider the 

 flowering plants one finds the number tolerant to a pyrophilous 

 condition greatly reduced. 



The importance of good drainage as an aid to rapid revege- 

 tation is quite evident from the preceding suggestion. If the 

 soluble concentrates produced by the fire are rapidly leached 

 away reversion, with a steady and progressive plant invasion, 

 will take place. But if, on the other hand, these concentrates 

 are held in the soil a retardation of plant development is to be 

 expected. 



I have personally observed several instances of mass inva- 

 sion by Marchantia polymorpha following forest fires in the 

 Rocky Mountain region of western Montana. These invasions 

 occurred in closely protected mountain meadows that were 

 surrounded by steep slopes, and at elevations of from 3,500 to 

 6,500 feet. In each case they followed severe fires that com- 

 pletely denuded the meadow areas and scattered desolation 

 over hundreds of acres through the hills. 



In order to effect such a wholesale invasion as occurred in 

 these instances, where an acre or more was covered with a prac- 

 tically pure stand of Marchantia, two important factors seemed 

 very essential. These necessary factors are the presence of a 

 considerable amount of humus and a soil having a high moisture 

 content during the period of growth and reproduction. The 

 mountain meadows to which I have referred had a deep gravelly 

 soil that contained a large quantity of humus. Deep snow fields 

 and the early rains of spring convert these into marsh-meadows 

 during the early growing season. Fall rains supply sufficient 

 moisture to insure fall growth and the development of spore 

 producing organs. The excessively dry summers of this region, 

 though causing a temporary dormancy, are apparently no 

 deterrent to the ultimate growth of this plant. Marchantia is 

 peculiarly adapted to withstand excessive dryness in its vegeta- 

 tive state, and recovers a normal condition quickly with a re- 

 newal of humid conditions. It should be noted here that Mar- 

 chantia was not found on the adjacent, steep, gravelly slopes. 



