70 



DISCUSSION 



It can be readily seen from the table that a cover of Cladonia 

 prevented as rapid an absorption of rain by the soil as was pos- 

 sible in open areas. The rain falling upon the mat was absorbed 

 by the lichen cover which swelled and held as much as 4^ 

 times its own dry weight before allowing moisture to pass freely 

 to the soil beneath. In one case 16 grams of dry Cladonia 

 weighed 73.5 grams when wet. When the rain was short and 



Table I 





Bed No. 



Soil Moisture 







Open 



Cladonia 



Notes 







Per cent 



Per cent 





July 5 



1 



5 .35 



1.78 



Light rain (2 hours) 





2 



5 .35 



1.78 





July 6 (a.m.) 



1 



8.92 



6.07 



Light rain (12 hours) 





2 



8.16 



5 .35 



1 .41 cm 



July 6 (p.m.) 











7:25 







5.35 



Light rain 



.96 cm. 



7:35 







5 .35 





7:45 (peak) 







8.92 





7:55 





16.78 



7.14 





July 26 (Before rain) 







1.78 



Light rain 



(After rain) 







1.78 



.41 cm. 



July 30* 







42.84 



Between rains 

 Big Stone Bay 



Aug. 8 









0.36 



Dry spell 



Aug. 9 









0.71 



Dry spell 



* This area is subject to moisture and wind from Lake Michigan. 



light, no moisture at all reached the soil. From the figures given 

 in the table, 2.26 times as much moisturewas found on the aver- 

 age in the open areas as under Cladonia mats after rains. 

 This prevention of the rain from reaching the soil easily e.x- 

 plained the drying up of the seedlings which germinated be- 

 neath the Cladonia and of those which germinated within the 

 Cladonia and became rooted in the soil beneath. 



On the other hand, it is true that the Cladonia tends to 

 hold whatever moisture there is present in the soil for a longer 

 time than the moisture remains in a similar but open soil. The 

 average amount of moisture found in the surface soil under the 

 lichen cover was under 1 % during dry spells, while in open areas 



