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the forests which ultimately clothe these lower slopes is attested 

 by the presence of such trees as Acer saccharum, Betula lutea, Tilia 

 americana, and Tsiiga canadensis; also by the frequency of many 

 mesophytic shrubs and herbaceous plants elsewhere uncommon 

 in upland woods. Such, for example, are Actaea rubra, Asarum 

 canadense, CaidopJiyllum thalictr aides, Dicentra Cucullaria, Ge- 

 ranium Rohertianum, Samhucus racemosa and Staphylea trifolia. 

 A further step in the reclamation of the talus by vegetation is 

 seen in the appearance of a belt of trees along the upper margin 

 of the slope. Here, under the very shadow of the precipice, is 

 usually a narrow zone where earth and finer rock particles, dis- 

 lodged from the clifT overhead, collect in sufficient quantity to 

 favor rapid colonization by plants. Moisture relations, however, 

 are poorer than at lower levels, so that a truly mesophytic vege- 

 tation is slow to develop. The belt of forest which fringes the 

 upper margin of the talus shown in fig. 4 consists largely of 

 chestnut oak and black oak. But the condition shown in this 

 photograph is by no means permanent. For, as the blocks of 

 rock midway up the talus gradually disintegrate and soil collects, 

 the two belts of forest encroach upon the barren area which 

 separates them, and ultimately the entire slope becomes wooded'. 

 The first plants to appear in the talus succession are lichens, but 

 their influence on later stages is negligible, for they are confined 

 principally to the rock face while the transformations that cul- 

 minate in the formation of forest are brought about almost en- 

 tirely by crevice plants. Crevice mosses doubtless aid in the 

 accumulation of soil and humus, and many of the crevice plants 

 previously noted are also present here; but the first conspicuous 

 crevice stage on talus slopes is usually dominated by vines and 

 shrubs. The shade produced by trailing vines such as Celastrus 

 scandens, Psedera guinguefolia, and Rhus Toxicodendron may be 

 a factor of considerable significance in hastening the advent of 

 mesophytic conditions. Characteristic pioneer shrubs are Cornus 

 circinata, Riihus odoratus and various species of Rhus. The shrubs 

 and vines are accompanied by trees, but except toward the top 

 of the slope there may never be a xerophytic pioneer tree stage, 

 for among the first trees to appear may be mesophytic species 



