1908] CURRENT LITERATURE 7. 
with slightly raised purplish margins, which attain a diameter of 3.5 to 13™™. 
The mature spots are usually circular, but may become irregular. This disease 
has been variously attributed to Phyllosticta, Coniothyrium, and other causes. 
The present authors obtained pure cultures of S phaeropsis malorum from all young 
spots which were studied. From older spots other fungi were obtained. 
Tnoculations with this Sphaeropsis produced typical disease in 5-20 days upon 
eaves. The fungus causing the leaf spot in nature is probably derived from 
cankers on the branches which are frequently abundantly infested.—F. L. StEvENs. 
Peat.—From the Geological Survey of Michigan there has recently appeared 
a volume on peat.?® The work consists of three separate essays under the fol- 
lowing titles: The ecology of peat formation in Michigan; The formation, 
character, and distribution of peat bogs in the northern peninsula of Michigan; 
Economics of peat. The author presents a classification of the Michigan peat 
deposits based upon (2) form of land surface, (6) method of development, and 
(c) surface vegetation, in which he seems to follow previous authors. e place 
taken by plants in peat formation depends directly upon their specific ecological 
demands, hence the floristic diversity which appears in the formation of peat in 
shallow depressions, upon flat areas and raised surfaces. Applying this principle, 
a thorough study is made of Mud Lake, which lies in the southern peninsula, and 
the successions are well traced out. The conclusion is reached that light is the 
Principal factor controlling the development of peat through its limiting influence 
on the growth of plants, both below and above the water level. Physical and 
chemical characters of the substratum, temperature, aeration, mechanical and 
Physiological effects of the wind, and competition are considered cooperating 
but secondary factors influencing peat development. 
In the second essay the northern peninsula is made the basis of study, and 
the vegetation of a large number of lakes and ponds is described in some detail, 
and the conclusions reached from the study of the southern peninsula substan- 
A comparison of the conditions found in the two peninsulas leads to the 
Statement that the noted variety of the sedge zone in the north is to be related to 
the fact “that in the cooler, more humid climate of the north, the shrubs men- 
Hioned are able to grow better in the water than they can in the south.” Froma 
Study of “Algal Lake,” a type of peat hitherto unrecognized, in this country at 
least, must be added to those which were known before, namely, algal peat, formed 
7 
almost entirely of the remains of one-celled or few-celled plants 
+0 part Tis appended a detail map of the original swamp area of the southern 
Peninsula; while part II is likewise accompanied by a map of the original vege- 
‘ation of the upper peninsula. These maps should prove of great service, both 
in this field and as a permanent record of a vegetation too fast suffering de- 
struction, 
DAVIS, C. Ac, “Peat: Fecan: the report of the Geological Survey for 1906. 
PP. 95-395. Lansing. 1907, 
