464 BOTANICAL GAZETTE [june 



less material of this kind where the juniper is absent. The com- 

 petition with shifting sand is nearly absent unless the dune is being 

 rejuvenated. The deposit is so slight that it does not seem to retard 

 either the germination of spores or spread by vegetative growth. 



The two mesophytic transition regions from conifer to oak 

 offer nearly as favorable moss habitats as do the pine slopes. Many 

 of the species are relics from the more shaded former conditions, 

 but which now are losing out, largely it would appear by encroach- 

 ment of other light tolerant mosses, rather than because of competi- 

 tion with herbaceous plants. The shade is much less, especially 

 during late fall and early spring. Many of the mosses are scarcely 

 evident during midsummer. Most of them produce many spo- 

 rophytes and mature the spores early in the year. That the 

 relative humidity is at times increased by nearness to the water 

 was quite evident on several trips to Miller when the weather 

 previously had been warm enough to raise the temperature of the 

 water of the Calumet. A strong cool wind from the north carried 

 the mist, which was ascending from the river, directly over the 

 transition slope. It was not learned how frequently this happens, 

 but a considerable amount of moisture must be deposited during 

 even a few hours of such a mist. This difference in humidity and 

 water supply is probably one of the chief causes of variation in the 

 . luxuriance of the mosses on these slopes and on those farther from 

 the lake, and not in the vicinity of other bodies of water. The 

 evaporation rate at other times is very likely higher than on the 

 pine dune, but unfortunately there are no data for evaporation on 

 these transition slopes. Neither competition with other plants 

 nor movement of sand is a very important factor, unless it may be 

 the latter near the top of the slope. 



On the oak dunes we again have an evaporation rate higher 

 than that of the pine dune, except in midsummer. The sparse 

 undergrowth in many places gives little protection from the 

 hot sun which penetrates through the foliage of the oaks. 

 During the spring and fall there is great exposure to somewhat 

 desiccating winds. On many of the more mesophytic northward 

 slopes where mosses might be expected there is often a dense 

 growth of vernal herbaceous plants which seem to have crowded 



