CHAPTER XIII. 



THE MORPHOLOGY OF WEEDS 



The Root. In the higher plants we are usually able to 

 make out three conspicuous organs, namely : The root, 

 stem and leaf, and at certain stages of development, a 

 fourth organ, the flower. The root, stem and leaf have 



to do with the nutrition of the 

 plant and the flower with its re- 

 production. In our study of a 

 type plant, let us begin with the 

 root. Roots naturally occur in 

 the ground; they fix the plant in 

 the soil and absorb water that 

 holds in solution certain mineral 

 constituents. The root increases 

 in length from a point just back 

 of the tip, growth taking place at 

 this point. The tip of the root is 

 and is contin- 



Fig. 35. Fibrous root of 

 crab grass. 



called the root-cap 

 ually wearing away, while new cells are 

 as constantly being added from the 

 growing point. Not far from the tip 

 also are the root hairs, which absorb 

 moisture from the soil. These become 

 covered with particles of sand, because 

 the cell walls are mucilaginous. 



There are four types of roots, classi- 

 fied according to duration : Annual, win- 

 ter annual, biennial and perennial. In 

 plants with annual roots, the seeds 



germinate, the plants produce flowers , Fi S; 3 6 - Root - ft 

 , , , ,. showing root cap. 



and seeds the same season and then die. (Leavitt.) 



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