216 THEO. J. STOMPS 



many species are common to both xerophytic and swampy lo- 

 calities, must be looked for in quite another direction. Inthe 

 first place I rather believe, that true swamp-plants, such as 

 Polygonum Amphibium, that are able to thrive under xerophytic 

 conditions, are extremely rare and only can do so by means of a 

 double adaptation. Most of the plants in question — Salix re- 

 pens also for instance — probably are typical of xerophytic life- 

 conditions. These species are able to thrive on a swampy soil 

 as well as in a botanical garden, if the struggle for existence with 

 other swamp-plants be not too intensive. This is rarely the 

 case, as a swampy soil is generally very poor in nutriment, which 

 must exclude, of course, many species. If we further take into 

 consideration that the xerophytic types in question are accus- 

 tomed to bad life-conditions themselves, it can really not cause 

 surprise that we meet them now and then in swampy places. 

 In this way I believe that we must understand the phenomena 

 just described, though I will not decide, of course, whether the 

 swamp-plants growing on the dunes of Lake Michigan, are origi- 

 nally oxylophytic or xerophytic types. Coming to a conclusion 

 I may perhaps say, that the main result of our visit to the dunes 

 of Lake Michigan has been, that we got a better understanding 

 of the value of the adaptations of halophytes, xerophytes and 

 swamp plants. 



