42 BOTANICAL GAZETTE [july 



they do not occur in a humous layer, and in humus the roots are 

 longer than in sand. 



Several species found more or less frequently on the open 

 sand, but especially along the borders of forested patches being 

 blown out, have in general similar characteristics, and will be 

 described together. These are Thuja occidentalis, Cornus stolonif- 

 era, Arctostaphylos Uva-ursi, Vitis spp., Betula alba, Tilia ameri- 

 cana, and Juniperus horizontalis. These rarely germinate on the 

 open sand, although Thuja and Betula alba are occasionally found 

 germinating on the edges of blown out patches, and regularly 

 germinate, when present, on the floor of these same patches. A 

 study of their root systems shows that the roots regularly follow and 

 exploit the carbonaceous layers and old soil lines, and the plants 

 remain stunted unless their roots find such plant remains. 



Populus deltoides. — This species is very rare in this region, and 

 its ecological equivalent, P. balsamifera, is found sparingly along 

 the shore of Lake Michigan, more frequently on Crystal Lake 

 beach, and in the burned part of the forested dune area. 



Salix spp. — The willows were not included in this study, 

 although their roots were frequently met, and certain points may 

 be noted. They showed a positive and vigorous hydrotropism, 

 which was observable in the neighborhood of pannes and also of 

 Lake Michigan. Several times roots were found descending with 

 the slope of the surface of the sand until they finally entered the 

 water table and passed under the pool in the panne. They also 

 show in marked degree the ability to form a small bunch of closely 

 branched rootlets in small dark patches in the sand. 



GENERAL OBSERVATIONS 



Root systems in glacial gravel layers. — In the blown out portions 

 of the Crater group gravelly layers of the glacial substratum had 

 been laid bare and bore a scattered vegetation similar to that of 

 the dunes. There was some excavation of Prunus puniila and of 

 Artemisia in this locality, and indications seemed to point to a 

 closer and more regular branching. There were of course no 

 buried plant parts, so that asymmetric development would not be 

 expected (fig. 14). 



