214 THEO. J. STOMPS 



dunes. A mighty impression they make, those enormous vol- 

 umes of rolling sand. 



And that they are mighty can be seen, when they encroach 

 upon swamps and forests, which they meet on their way, cover- 

 ing them up as they go. Nothing is then able to resist their 

 power. We were lucky enough to see something of this encroach- 

 ment on preexisting plant societies near Dune Park and Sawyer. 

 About these observations, however, I will not enter into a lengthy 

 discussion. Dr. Cowles has done this in an excellent way in his 

 The Oecological Relations of the Vegetation on the Sand Dunes 

 of Lake Michigan. 1 There is one point, however, which I should 

 like to mention here. It is the behavior of certain swamp-plants, 

 such as the willows and the red osier dogwood, Cornus stolonifera, 

 when a moving dune is encroaching upon them. This behavior 

 can very easily be understood by one who is acquainted with the 

 habits of Salix repens, which is quite common in the dunes and 

 swamps of Holland. He knows that Salix repens occurs in two 

 types, the one on moist soil, standing erect, the other on slopes 

 of dunes, crawling along the ground. So different are these two 

 forms, that one might feel inclined to consider them as distinct 

 elementary species. Still, that this assumption is unfounded is 

 shown by the following observation. In order to prove this let 

 us see what happens, when a moving dune has approached to 

 the above named swamp-plants and begins to cover them. The 

 erect habitus is lost and they begin to creep along the slope of 

 the advancing dune, in the meantine shooting roots from their 

 branches. This holds good of the willows as well as of Cornus 

 stolonifera. Thus we see that these plants are able to leave their 

 swampy localities and to adjust themselves to the dry conditions 

 of the sandy slopes and this behavior is exceptionally important, 

 because it enables the plants in question to partake in a powerful 

 manner in the capture of an actively moving dune-complex by 

 vegetation, in other words in preparing the dune-soil for the 

 development of the pine-dune-association. But to the botanist 

 this behavior is still more interesting from another point of 



1 Bot. Gaz. 27, 1899. 



