76 Principles of Plant Culture. 



by roots is generally less than their greatest horizontal 

 extent. The distance reached by the deeper roots is 

 probably governed largely by the nature of the subsoil 

 and the depth of free ground water. But in most annual 

 crops a comparatively small part of the root system de- 

 velops much below the plow line. At the Geneva Ex- 

 periment Station * the chief root- feeding ground of the 

 field and garden crops grown in that locality appeared 

 to be from three to ten inches below the surface, while 

 that of crops making large development of stem and foli- 

 age during summer, as Indian corn, sorghum, tobacco 

 and the Oucurbitse, appeared to be shallower than in 

 slower-growing crops. 



A portion of the roots of many croj)S grow very near 

 the surface of the ground. Branches from the main 

 horizontal roots often grow upward as well as in other 

 directions. At the Geneva Experiment Station, numer- 

 ous roots of sweet corn were found within an inch of the 

 surface, and in a tall-growing southern corn, roots of con- 

 siderable size started at a depth of only half an inch. 

 The main root of a Hubbard squash vine was traced a 

 distance of ten feet, in which its depth varied from two 

 to five inches. In tobacco fields, the rootlets sometimes 

 literally protrude from the surface of the soil in warm, 

 wet weather (232). 



III. The Rate of Root Growth in rapidly developing 

 plants is often extremely fast. President Clark, formerly 

 of the Massachusetts Agricultural College, concluded 

 from very careful examinations and measurements of the 

 roots of a squash vine grown under glass, that rootlets 



* See Report of New York Agricultural Experiment Station, 1886, p. 166. 



