282 



Minnesota Plant Life. 



water, as, for example, the marine eel-grass, so common along 

 seashores around the world. This plant is famous for its de- 

 velopment of thread-shaped pollen-spores a form more favor- 

 able for aquatic pollination than the ordinary round spores 

 common in most other plants. There are no flowering plants, 

 however, which are so strongly adapted to the aquatic life as 

 are the riverweeds. Even the tiny duckweeds, floating like 

 green specks at the surface of quiet pools depend upon the wind 

 for the distribution of their pollen and produce their pollen sacs 

 and stigmas in the air as did their terrestrial progenitors. 



Stone-crops. The orpine family is represented in Minnesota 

 by the native stone-crop 

 and the introduced u hen- 

 and-c hick ens." The 

 stone-crop, which grows 

 in ditches and swamps, is 

 a slender, erect plant with 

 smooth leaves and stem. 

 The flowers are produced, 

 at the tip of the stem, in 

 cymes on recurving 

 branches from one to 

 three inches in length. 

 The flowers have five se- 

 pals, ten stamens, usually 

 no petals, and five rather 

 imperfectly fused carpels 

 in each of which a num- 

 ber of seed-rudiments are produced. Many of the orpine fam- 

 ily are rock-dwelling plants and belong to the adaptational 

 group known as leaf-succulents. The "hen-and-chickens" is an 

 example of this group. Its leaves are very fleshy and thick, often 

 grayish-green in color and arranged in rosettes, from the centre 

 of which the erect, central flowering stems are developed. Such 

 plants inhabit little crevices in cliffs, and the fleshy character of 

 the leaves is doubtless in response to the difficulty of obtaining 

 sufficient moisture for the roots. The ditch stone-crop, how- 

 ever, prefers moist places, and has leaves of quite ordinary ap- 

 pearance. 



FIG. 137. American alum-root. After Britton and 

 Brown. 



