790 



A TEXTBOOK OF THEORETICAL BOTANY 



planted with others in conventional drills the length is reduced to half to 

 one-third of a mile. The growth of weeds, especially Charlock, may reduce 

 the amount to one-fifth or one-tenth of this. Such figures enable us to 

 realize the intensity of the competition which must exist between the roots 

 of plants living in a close community and how valuable to a plant may be 



40 



r 



20 



OCms 



20 



40 



60 



,,-J^ 



6 



80 



f 



100 



Fig. 785. — Types of root systems. A, Taraxaciwi officitiole. Taproot system. B, Poa 

 secunda. Fibrous root system. Monocotyledon. C, Achillea lamdosa. Fibrous 

 root system. Dicotyledon. {After Spence.) 



any peculiarity of rooting, e.g., exceptional depth, which may enable it to 

 escape some of this competition. 



It was mentioned above that the root systems of Monocotyledons differ 

 from those of Dicotyledons. This is due to the early abortion of the main 

 root, which disappears soon after germination in the great majority of 

 Monocotyledons. 



In some cases, notably among the Grasses, it may never be formed at all 

 or may abort before germination. The whole root system of the plant 



