505 
An examination of the three views ot the moors suffices to con- 
vince anyone that in the same sense that zones of Carex, Phrag- 
mites, Scirpus, Nymphaea, Potamogeton and Chara are described as 
characteristic of the limnetic distribution in the lakes of the Jura or 
elsewhere, so also are zones of Larir, Picea, Ledum, Andromeda and 
Utricularia, characteristic of the filled lakes or moors of Minnesota. 
: It is scarcely worth while to designate the zones as Laricetum, 
Picetum, etc., for an indefinite number of such names might be 
found necessary in different parts of the world. 
Certain points that have been touched upon might rightfully 
claim a more extended discussion. The presence of the spruce 
between the tamarack and the moor is peculiarly interesting. 
Large numbers of these muskeags form no spruce ring at all. 
This is especially true of those towards the southern limits of the 
formation, as for example near Minneapolis, which is south of the 
black spruce belt in Minnesota. In such cases the tamarack trees 
themselves stand facing the moor, and the transition is through 
Salix, Cornus, Ilex and kindred shrubby plants. A number of 
views illustrating this type of tension-line between moor or meadow 
and tamarack swamp have been obtained and may be published 
later. Apparently the exact habitat offered outside the sphag- 
num and inside the larch zone is seized upon by spruces, and they 
establish themselves where the water is too cold or the soil too 
thin for the tamaracks to flourish. : 
Cedar swamps offer a number of ecologic conditions that can 
not be entered upon here. Combinations of cedar and spruce in 
the tension line surrounding muskeag are met with. Their study 
is deferred until later. 
In the case of the spruce trees established in their zone periph- 
€ral to the Zedum formation, the gradations in size connected as 
they are, under the reservations made above, with gradations in 
age, indicate that the tamarack and spruce rings are slowly closing 
in upon the central formations and should eventually occupy the 
Whole area of the moor to the exclusion of those plants which 
flourish in the open. Asa matter of fact, such circular or ellipti- 
cal tamarack formations, solid clear to the core, are frequent in 
southern Minnesota, while in northern Minnesota a slight variation 
arises from the ordinary presence of a small central group of 
