ON ROCK 217 
of the segments striped with yellow, is one of the most characteristic 
of moist ,;woods, while others (Geophilus rubens and Lysiopetalum lac- 
tarium)_are not uncommon. Ground beetles (Calathus gregarius Say) 
and bugs (Reduviolus subcoleoptratus) occur. In logs of fallen basswood 
we found the larvae of Tenebrionidae and Cerambycidae and of horntails, 
the burrowing hymenoptera, and the Mycetophilidae larvae (Sciara) 
(Fig. 174) (165). 
c) Field stratum and shrub stratum.—The field stratum has been but 
little studied. We have taken a few Scudderia nymphs, some spiders, 
and bugs, but no adequate study has been carried on. 
d) Tree stratum.—This has likewise been but little studied, but in 
these young forests, while the ground stratum is like that in the older 
forest, the tree stratum is poorly de- 
veloped because the trees are short 
saplings. As time goes on, however, 
the forest becomes more dense. Such 
a forest may be seen on the bluff at 
Lake Bluff, Ill. 
5. OTHER BARE CLAY FORESTS 
Other bare clay young forests may 
be seen along the dumps of the drainage 
and Chicago-Michigan canals at Summit. 
Here we find practically the same stages 
as at Glencoe on the lake bluff. There Fic. 174.—One of the fungus 
are the steep clay bluffs with no perma- gets SOU E PeL re eae 
% : which are commonly found under 
nent residents, the semi-stable bluffs, or the hark of trees, feeding on fungus. 
weed-occupied areas. These are like the 
semi-stable bluffs at Glencoe but the tiger-beetle is another species and 
selects more nearly level places; otherwise it is very similar in habits. 
The shrub stage occurs but is without the snails, since the ground- 
water level is lower and the moisture in the soil of the lake bluff is wanting 
here. This causes the development of the ground stratum to lag behind, 
while it is in advance in the bluff forests. Accordingly we find a sapling 
forest made up largely of cottonwoods. This has not been studied. 
III. Forrest CoMMUNITIES ON Rock 
(Station 55) 
The rock exposures near Chicago are not numerous, and we have 
studied only those at Stony Island. There the bare rock is inhabited 
