176 Minnesota Plant Life. 



Scouring-rushes with two sorts of erect stems. In a few 

 of the species there are formed two kinds of erect stems. One 

 is pale or reddish in color, softer to the touch, provided with 

 longer leaves below the cone, devoid of leaf-green and de- 

 voted to the work of spore-production. The other is repeat- 

 edly branched, the branches arising in circles at the top of 

 each joint of the stem. Upon such erect stems no cones 

 are ordinarily displayed, but the whole plant-body is 

 green and starch-producing. Both kinds of erect 

 branches are, however, very similar in internal struc- 

 ture. They are hollow and their wood-threads are ar- 

 ranged in a circle, usually with air-canals between them 

 and within them. At the top of each joint a group of 

 leaves arises in a ring. These are not used for starch- 

 making but are reduced and scale-like and commonly 

 blended together by their edges into a collar closely 

 enveloping the lower part of the joint immediately 

 above. On the special spore-producing branches the 

 leaves are often larger and less completely fused to- 

 gether. Sometimes the leaves are black in color with 

 gray tips, as in a well-known joint rush of Minne- 

 sota. In all the varieties the starch-making is done 

 not by the leaves but by the branch-system, so that in 

 this respect the plants resemble the well-known aspar- 

 agus, to which they bear, however, no close botanical 

 relation. 



When the spore-cases on the shield-shaped leaves 

 open to eject their spores, the spores may be shaken out 

 into the hand as a green dust. If one watches this dust 

 as it lies upon the hand immediately after 



JIG. 67. A fruiting stem 



of the horse-taii. having been shaken from the cone, it will be 

 s e re-a e rtagtTe d s seen that within a couple of seconds after its 

 are aggregated in a deposit it fluffs and becomes of 3. lighter 



cone. After Atkin- . . 



son. color. By warming it gently with the breath 



it regains its darker hue and more solid ap- 

 pearance, but in a couple of seconds it fluffs again as it did 

 before. This remarkable behavior is explained if the spores be 

 examined under a good microscope. It will then be observed 

 that apparently attached to each of them are four delicate spoon- 



