73 



Heracleum lanatum Michx. Cow Parsnip 



Impatiens hiflora Walt. Spotted Touch-me-not 



Impatiens pallida Nutt. Pale Touch-me-not 



Polyganum virginianum L. Virginia Knotweed 



Symplocarpus foetidus (L.) Nutt. Skunk Cabbage 



Urtica gracilis L. Stinging Nettle 



Laportea canadensis (L.) Gaud. Wood Nettle 



Viola papilionacea Pursh Purple Violet 



A general summary of the distribution of the most typical 

 marsh birds, showing where each finds its optimum conditions 

 for nesting, is shown in Plate VII. The extent of range is 

 indicated by the length, and the optimum conditions by the 

 greatest width, of the black lines. 



Succession. 

 Even the most casual observer who has had opportunity to 

 revisit a marsh after a short absence, is struck with the 

 changes that have taken place. One cannot help noticing 

 that conditions are far from static. Aside from such radical 

 changes as occur when a stream alters its course, or when a 

 barrier breaks and produces a flood, there are certain forces 

 always acting, which place each association under a sort of 

 tension. These forces are the struggle for existence and, 

 especially, the struggle for the perpetuation of kind. Each 

 zone tends by its growth to increase the area which it occupies, 

 and therefore crowds upon some other society. The bulrush, 

 extending further and further from shore, gains a foothold 

 where before it was impossible for it to live. The tangle of 

 its roots and the denseness of its growth, which naturally 

 follow nearer the shore, furnish the shelter which is necessary 

 for the life of the other plants of the shore line. These in turn 

 crowd into the bulrushes, and even by so doing render condi- 

 tions more favorable for themselves and less so for the former 

 occupants. The innermost of the bulrushes die, and that zone 

 has been crowded forward. While this has been in progress, 

 a similar struggle has been going on between the vanguard of 

 the cat-tails and the rear guard of the shore-line association, 

 resulting in the crowding of the latter further from the shore. 



