HARPER: PLANT POPULATION OF MICHIGAN 29 
by either marsh or bog vegetation (corresponding to Warming’s 
“low moor” and “‘high moor”’ respectively.*) 
The most significant difference between marsh and bog vege- 
tation (and one apparently overlooked by Warming in contrasting 
his low and high moors) is in the rate of growth; and just why 
rank grasses should occupy one pond and the slow-growing sphag- 
num, evergreen shrubs, and stunted conifers another has never 
been fully explained. The depth of the water undoubtedly has a 
great deal to do with it, for a shallow pond is quickly warmed by 
¢ A 
Fic. 2. Looking north across a oe —— or sedgy pond, with stagnant 
water quite warm in summer, a sort of “low moor’’, 20-25 acres in extent, about 2 
miles southeast of Douglas Lake. Vegetation coms Carex filiformis, with a few 
wand Lams of Chamaedaphne and Andromeda. Partly burned conifer swamp 
n background. = little to the left of this view, near a moderately rich hillside, 
e ra therefore faster-growing vegetation, including Calamagrostts 
me ran 
canadensis, ne peg Sparganium, and Iris versicolor.) 
the sun, and one in Michigan, where the sun shines nearly sixteen 
hours a day in midsummer, may be nearly as warm during the grow- 
ing season as one in Florida, where there is not more than fourteen 
hours of sun ina day. Furthermore, a deep pond, besides being 
colder, may be too deep in the middle for aquatic plants rooted in 
the soil (such as the Nymphaeaceae) to reach the surface, so that it 
* See his Oecology of Plants (1909), pp- 196-199, 200-205. 
