32 STUDY OF COMMON PLANTS. 



3. Examine under a lens the structure of a blackberry 

 root, or that of some other common woody plant. 

 Cut a transverse section, and notice the position 

 of the wood elements. Compare this with their 

 arrangement in the stem. A little reflection will 

 show that the arrangement of the mechanical ele- 

 ments corresponds with the very different condi- 

 tions that obtain in root and stem. The former 

 must be so constructed as to resist a force that 

 tends to pull it out of the ground ; in the latter, 

 on the other hand, resistance to a lateral and ver- 

 tical force must be provided for. 1 

 Other roots should be examined in the same way. 

 Those of Indian corn seedlings will be found 

 useful. 



VII. Compare fully grown turnips and carrots, radish, 

 or salsify with the roots of seedlings of the same plants. 

 What changes of form and structure have they undergone? 



VIII. Study the formation of adventitious roots, as 

 seen in Verbena and other plants, grown by florists from 

 slips. Adventitious roots of Tradescantia can be obtained 

 by placing a fresh branch in a closed bottle so that the 

 cut end will stand in a little water at the bottom. 



SPECIAL STUDIES. 



I. Protection of the growing point of the root. A 

 number of water plants furnish excellent material 

 for microscopic study of the root-cap. Among 

 them are Lemna minor, common everywhere in 

 stagnant waters, and Pontederia crassipes, fre- 

 quently grown in artificial ponds. Certain aerial 



1 Cf. Haberlanclt, Physiologische Pflanzenanatomie, p. 125 ct seq. 



