46 ECOLOGICAL RELATIONS OF THE FLORA. 



Cakile edentula. 

 Arahis lyrata. 

 Artemisia caudata. 

 Triglpchin viaritima. 

 Salsola kali. 

 Xanthium echinatum. 

 Potentilla anserina. 

 Cirsium pitcheri. 

 Cenchrus tribuloides. 

 Physalis heterophylla. 

 Echinocystis lobata. 



Dune Formation-Calamovilfa-Ammophila Association : The upper 

 beach, the upper and lakeward side of the outermost dune, was clothed 

 with easily the most distinct association on the Point. This close 

 organization was holding the sand, was withstanding the sand storms, 

 and was persisting under the competition of the plants of the jack 

 pine ridges. (Plate II a.) In fact the assault was from two sides, 

 for the water currents and winds were lodging the common weed seeds 

 — Amaranthus, Salsola, Chenopodium, and the asters and golden rods 

 — on the middle beach, from whence they tended to invade the dune 

 face. 



It is not necessary to describe this beach in detail. It belongs to a 

 type that exhibits relatively little variation around the Great Lakes. 

 The edaphic conditions are very severe. The clean lake sand of very 

 fine particles (81 per cent, .25 to .001 mm. in diameter, see Bull. Bureau 

 of Soils, 1901, p. 99), the absence of organic matter and the excess of 

 certain mineral elements are the common characteristics of the sub- 

 stratum. Cowles (1899) has pointed out, furthermore, that the xero- 

 phylly shown bj'^ the members of these formations is due not so much 

 to the lack of water in the soil as to the xerophyllous air. In such 

 places the light is most intense, the heating effects are greatest and 

 the drying action of the wind most vigorous. King (1900, p. 230) 

 records that the drying effect of the wind 300 feet from a hedge row 

 was 24 per cent greater than near the hedge. In a similar manner 

 the absence of all shrub-like plants or wind-breaks on the outer face 

 of the dune permits excessive dessication here. 



To this should be added the effect of great diurnal variations, as 

 only a plant fitted for xerophyllous conditions can adjust itself to 

 high temperatures in the day time and very low ones at night. 

 Maximum and minimum temperatm-es for the open beach and deep 

 woods were taken for July. (See appendix.) These records are useful 

 in illustrating the fact that the beach was always warmer during day 

 time and colder at night than the deep woods. Alsp the difference 



