1912] SHERFF—SKOKIE MARSH 425 
polygonetum, where their rhizomes lie in common near or at the 
surface of the stream bed, they are “edaphically” (see WoopHEAD 
18) competitive, and hence complementary only in an aerial way. 
In this particular case, however, the frequently open appearance of 
the vegetation in the Sio-polygonetum indicates that the mutual 
biotic struggle of the two species is less keen than their separate 
struggles against somewhat adverse environmental conditions. 
In the reed swamp certain mints become conspicuous during 
midsummer, particularly so in the Scirpo-typhetum, where they 
thrive in the shelter of Typha and other tall plants. Teucrium 
occidentale and Scutellaria galericulata are very common. They 
produce from their basal nodes numerous slender stolons that run 
out at different depths in the soil, and these stolons may produce 
new plants. These species tend to have their root systems 3-6 cm. 
lower in wet situations than in dry, although exceptions to this rule 
are not rare. But whether growing from plants in dry or from 
those in wet situations, the new stolons exhibit a remarkable power 
of changing their direction of growth, in response to numerous 
obstructions, and thus they may proceed further without serious 
results. Considering the strength and size of the rhizomes of 
Typha, Sparganium, and Scirpus, also the delicate nature of the 
stolons of Teucrium and Scutellaria and their capacity for altering 
growth-direction, it is probable that mechanical competition 
between such rhizomes as those of Typha and such stolons as those 
of Teucrium is practically absent. Again, the aerial parts of the 
Typha form vegetate chiefly in higher atmospheric strata than 
do those of the Teucrium form. Evaporation readings show that 
in the higher strata evaporation is much greater. And while plants 
of relatively xerophytic structure (e.g., Typha, Sparganium, and 
Scirpus) are fitted to withstand acute drying conditions, plants with 
foliage of looser texture (e.g., Teucrium and Scutellaria) can vege- 
tate better in lower strata where the effect is that of greater humid- 
ity; the abundance of the latter plants among the former at Skokie 
Marsh tends to confirm this statement. Further, the persistence 
with which tall plants like Typha become dominant under favorable 
soil conditions shows that they are not, at least noticeably, harmed 
by plants like Teucrium. If, finally, we allow for the great avail- 
