222 MICHIGAN SURVEY, 1908. 



the bogs was strikingly slower. The rings of the bog species were in 

 many cases so close together as to render a. hand lens desirable for 

 counting them, while the annual rings of the' same species in the adja- 

 cent forest were widely separated. 



2. Shore Vegetation. The work done on shore forms was confined 

 entirely to the south shore, including the group of small islands near 

 the abandoned Light-house at Eock Harbor. The northern shore is steep 

 and cliflf-like, the southern shore gently sloping. While the northern 

 shore is strikingly different from the southern, and might have brought 

 to light many interesting things (especially in the way of lichen forma- 

 tions), it seemed best to confine the limited time at our disposal to work 

 on the south shore. 



Of the special shore forms, the crevice plants are both interesting 

 and attractive. The crevices in most cases are due to Assuring, although 

 some long, narrow grooves were made by the differential weathering of 

 the softer vein rock. The bed-rock of the shore is often amygdaloidal, 

 and many small depressions in this, due to the more rapid weathering, 

 afford a foothold for the hardy plants of the rock shore. In their narrow 

 rock crevices and confines, with little soil, and on dark-colored rock which 

 in summer becomes highly heated, at all times exposed to the strong 

 lake winds, and in winter often washed by the powerful storm waves of 

 Lake Superior, their struggle for existence is certainly a most strenuous 

 one. On the whole their size and appearance is strikingly alpine, as 

 is also their coloring in many cases. 



A partial list of the crevice plants is as follows : Campanula rotun- 

 difolia, Potentilla tridentata, Potentilla littoralis, Saxifraga tricuspi- 

 data, Saxifraga aizoon, Saxifraga nivalis, Artemisia canadensis, Senecio 

 balsamitae, Primula mistassinica, Solidago virgaurea (?), Sagina sag- 

 inoides, Achillea millefolium, Aster ptarmacoides. Sisymbrium humile. 

 JjOlielia halmii, Naiahis racemosa, etc. The insectivorous Pinguicula 

 ■vulgaris (Butterwort) occurs in rock pools and on wet rocks along the 

 Tocky shores." 



The most common crevice shrubs were the Juniperus nana, Juniperus 

 ■procumbens, Arctostaphylos uva-ursi (Bear-berry), Shepherdia cana- 

 densis (Shepherdia), Opulaster opulifolius (Ninebark). On the exposed 

 I'ocks at Scovill Point and at the eastern end of the island, the Empetrum 

 nigrum (Crowberry) was also found, forming a part of the heath mat. 

 Of all these the J. procumbens is easily of the greatest importance in 

 preparing the way for other larger forms of plants. Certainly no shrub 

 of Isle Eoyale precedes it or has better claims for pioneer distinction. 

 Its hardiness, prostrate manner of growth, and its thick, sheltering 

 branches are all of great importance in liiaking it an excellent pioneer. 



A study of the small rock islands near the Rock Harbor light-house 

 was very interesting not only on account of the striking differences in 

 the individual flora of each, but also for a comparative study of the plant 

 successions upon them. All stages of successions were noted from an 

 unusually rich mesophytic flora, growing on a humus soil 3-10 inches 

 in depth, down to islands almost bare except for a few crevice plants. 

 In general all the islands showed a less development of the flora on the 

 side exposed to the open lake than on the more protected land side: in 

 some cases the vegetation of the two sides was strikingly different. 



The advantages of crevice)^ in enabling vegetation to get a start upon 



