74 Principles of Plant Culture. 
reached by roots is generally less than their greatest hori- 
zontal extent. The distance reached by the deeper roots is 
probably governed much by the nature of the subsoil and 
the depth of free ground water. But in most crops on cul- 
tivated ground, a comparatively small part of the roots de- 
velop below the plow line. At the Geneva Experiment 
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 that make 
very large development of stem and foliage during summer, 
as Indian corn, sorghum, tobacco and the Cucurbite (42), 
appeared to be shallower than in slower growing crops. 
A portion of the roots of many crops 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, numerous roots of sweet 
corn were found within an inch of the surface, and in a tall- 
growing southern corn, roots of considerable size started 
out 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 sur- 
face of the soil, in warm, wet weather. 
111. 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 during the latter part 
of the growth period, rootlets must have been produced at 
the rate of at least one thousand feet per day. 
* See Report of New York Agricultural Experiment Station, 1836, p. 165. 
