ROOTS AND THEIR RELATION TO PLANTS 29 



rainfalls of the regions where 

 these plants grow. Others, as 

 the mesquite of the extreme 

 southwest, have roots that pen- 

 etrate into the earth to extra- 

 ordinary depths until they reach 

 moist soil. Still others for 

 example, many South African 

 plants (fig. 20), some wild 

 morning-glories, and the big- 

 root 1 of the Pacific coast 

 have fleshy roots in which much 

 water is stored. 



28. Water roots. Most aquatic 

 perennials, like the cat-tails, ar- 

 rowheads, pickerel weeds, pond 

 lilies, and many grasses and 

 sedges, form mainly earth roots. 

 On the other hand, some plants 



not aquatics for example, many willows can develop roots 

 indifferently either 

 in earth or in water. 

 Willows growing 

 along a brook usu- 

 ally send great 

 numbers of roots 

 into the earth, and 

 also produce a mul- 

 titude of fibrous 

 roots which dangle 

 in the water. Cut- 

 tings of Wander- FIG. 21. Duckweed, a floating aquatic plant 

 ing Jew (Zebrina), At left, top view of single plant 8 times natural size ; 



Cranium ( Pelarao- nt ri ht ' * rou P of three individuals of another species 

 ^eiarc/o r(>pre8ented fts floatlng> with root8 hanging vertically. 



nium), and many Three and one-half times natural size. After Prantl 

 1 Echinocystis. 



FIG. 20. A desert Pelargonium 

 (closely related to the common so- 

 called geraniums) 



Note the scanty leaf surface and the 

 fleshy root and base of the stem, con- 

 taining much water and reserve food. 

 After Andrews 



