r92t] JOHNSON—VIRGIN SOIL 309 
Ageratum conoyzoides L. (annual) 
Ageratum houstonianum Mill. (annual) 
MoNnoCOTYLEDONEAE Vernonia acuminata Less. (half shrubby) 
Arundo (saccharoides Gr. ?) Vernonia permollis Gleason (half shrubby) 
Mikania scandens L. (Wild.) (shrubby 
vine) 
Eupatorium triste DC. (half shrubby) 
Baccharis scoparia Sw. (shrubby) 
Pluchea odorata L. (Cass.) (half shrubby) 
Bidens incisa Ker. (annual) 
Senecio discolor (Sw.) DC. (shrubby) 
There were thus seven species of ferns, of which Dryopteris oligo- 
phylla, Blechnum occidentale, and Aneimia adiantifolia were rare, 
less than a score of each being seen where we crossed the valley. 
Pityrogramma calomelaena and Gymnogramme tartarica were more 
frequent; while Trismeria trifoliata was represented by dozens of 
specimens in the moister soil, and of Pteris longifolia there were 
still more numerous clumps in the drier spots along the trail across 
the valley. From the size of many of the fern plants seen it seems 
clear that they have been established for some time. In the cases 
of Gymnogramme and Trismeria, where fronds a meter high were 
seen, it was hard to believe that such plants could have arisen 
from a prothallus in nine years. Yet they must have done so 
unless it is assumed that old rhizomes have persisted in the soil 
to push up through the gravel, or that pieces of rhizomes have 
been washed down by the flood of 1909 or subsequent lesser ones. 
The first supposition seems negatived by the fact that no ferns were 
seen in 1910, six months after the flood, and also by the fact that 
each clump of a fern consists of but one or a few branches and 
leaf clusters. This latter feature tends to confirm the impression 
gained from the character of the soil, namely, that these ferns 
have started in situ from prothallia. 
All the seed plants found in the valley, except Arundo along 
the stream at the foot of the cliff, were dicotyledons. By far 
the most important of these was the composite Vernonia permollis. 
Scores of clumps of this, from quite young plants up to those 2 m. 
high, were found scattered across the valley. They grew beside 
the larger rocks and often also formed rather definite rows along 
