Minnesota Plant Life. 



455 



produce underground or prostrate rootstocks. These organs 

 are underground in sedges, scouring-rushes, reed-grasses, 

 sweet-flags, cat-tails, some of the cranberries, brambles and 

 primroses. They are above ground and prostrate in many of 

 the heaths and club-mosses. The tissues of swamp plants are, 

 as those of water plants, likely, in a variety of species, to be 

 spongy. Thus, the rootstocks of the cat-tail, the rootstocks 

 and stems of the scouring-rush. the leaves of many sedges and 

 the leafless erect stems of bulrushes contain a great number 

 of air chambers, giving them a spongy consistency. Some 



FIG. 25. Ferns in tamarack swamp. I y ake Calhoim. After photograph by Hihbard. 



swamp plants have special aerating organs, of which cypress 

 "knees" are examples. But these structures do not occur, so 

 far as I know, on any Minnesota species. 



Most swamp plants have adaptations for limiting the tran- 

 spiration of water from their shoots and leaves ; that is to say, 

 they are in this character like the xerophytes of desert regions. 

 Among the various devices for reducing transpiration may be 

 mentioned the hairiness of many swamp plants, such as the 

 swamp-saxifrage. Sometimes special pegs are produced around 



