Vegetation of Northern Cape Breton. 311 



confined, the character of the vegetation within the flood zone in 

 ravines is influenced to a marked degree by the abrading action 

 of the current at times of high water. Particularly is this true 

 along the larger streams (Figs. 17, 19), to which the following 

 remarks primarily apply. Woody plants, for the most part, are 

 either absent or sparsely developed and even the herbaceous 

 plants are scattered. The characteristic vascular plants of rocky 

 banks between high and low water levels are herbaceous peren- 

 nials, and these are mostly restricted to crevices and similar 

 situations where their perennating roots and rhizomes can main- 

 tain a foothold. Common species are Equisetum sylvaticum, 

 DescJiampsia flexuosa, Sagina procumbens, Campanula rotundi- 

 folia, Erigeron hyssopifolius, and Solidago bicolor, together with 

 various weeds, such as Prunella vulgaris, Achillea Millefolium, 

 and Chrysanthemum Leucanthemum. In addition to these, a 

 prominent position is frequently occupied by various bryophytes, 

 such species as Preissia quadrata, Fossombronia foveolata, 

 Marsupella emarginata, Nardia obovata, Hygrobiella laxifolia, 

 Grimmia apocarpa, G. conferta, and Racomitrium aciculare. 

 Toward the upper margin of the flood zone, skirting the lower 

 edge of the ravine forest, there is commonly a narrow fringe of 

 shrubs which constitutes a more or less distinct association-type. 

 The characteristic species here is Alnus mollis, with which may 

 be associated Salix humilis, Rubus pubescens, Acer spicatum, 

 Diervilla Lonicera, and other shrubs, together with such herba- 

 ceous mesophytes as Osmtinda Claytoniana, Phegopteris poly- 

 podioides, Strcptopiis amplexifolius, and Solidago latifolia. 



Conditions similar to those just outlined may prevail in ravines 

 along small streams, but here the stream bank vegetation com- 

 monly is such that it has seemed best to treat it under the 

 hydrarch series (see p. 368). 



Cliff association-types. — Certain pteridophytes are especially 

 characteristic of crevices in cliffs, well above the level of the 

 stream, notably Polypodium vulgare, Aspidium fragrans, Cysto- 

 pteris fragilis, IVoodsia ilvensis, and Lycopodium Selago. With 

 the exception of perhaps the last-named species, these grow best 

 in moist, somewhat shaded habitats. Various of the herbaceous 

 perennials of the flood zone are equally common here, particularly 

 Deschampsia and Campanula, while the crevice plants mentioned 

 earlier in connection with the rock outcrop series of ordinary 



