36 



exception rather than the rule and many shallow-rooted 

 species develop their root-systems entirely within the 

 surface foot or eighteen inches of the soil. 1 Probably 

 this really is due in part to the better aeration of the 

 surface soil but it is not, in itself, evidence to that 

 effect. For instance, Cannon^ has shown that in some 

 species the habit of shallow rooting is a response to dif* 

 ferences in soil temperature. Furthermore deep-rooted 

 plants, though not so common as those of shallow habit, 

 are plentiful and occasional cases of extreme depth have 

 been recorded. Thus Rotmistrov 3 says that roots of 

 Alfalfa have been found at a depth of 70 feet (21 m. J • 

 Bessey 4 recorded roots of lupine at 60 to 70 feet (18 

 to 21 m. ) in the dune lands near San Francisco. Hilgard 



1. See especially Gannon,- loc. oit . (Pub. 131). 



2. Oar. Inst, of Wash., Yearbook 13: 81-82, 

 93-96, 9 6-97 (1914); Science,- 41: 173-174 (1915); 

 Amer. Jour. Bot. 2: 211-224 (1915). See also Tolsky,- 

 Zhur. Opyt. Agron. 2j_ 733-744 (1901). 



3. Root Systems, p. 3 (1909). 



4. Quoted by Todd,- Proc. Amer. Asso. Adv. 

 Sci. 27: 238 (1878). 



