Studies OF Heauth in Potatoes. 
13 
would not gro,w potatoes perinanently. At Ames, Iowa, in the late 
summer of 1914, Mr. E. E. Isaac, a graduate student, and the writer 
dug two large holes in a potatC) field, which has a good deep loam 
but which is underlaid by clay and which requires artificial drainage. 
We found, in gravelly loam, potato roots dead at 4 feet, and stand¬ 
ing water at 4}^ feet; and in heavy clay loam, roots were dead at 
35/2 feet with water at 4^ feet. The closer-grained soil drew to 
a higher level water enough to drown the roots. This condition 
was found in 1912 at Del Norte, Colorado, where a rise in the Rio 
Grande River had raised the water level under the potato field. 
Laboratory studies ol potato roots throw an interesting light 
upon the field studies. The potato root, in the conditions studied, 
penetrates raw clay soils not at all. This, doubtless, is not only 
because in such soils a potato root does not find the amount of air 
which it needs, but also because its root cap (C in Figures 4, 5 and 
6) is an inefficient protection to the growing tip of a penetrating 
root. Doubtless potatoes have grown for so many ages in an open 
soil that their roots are adapted neither to enter nor to live in very 
close-grained soils. We find that the root cap loses large masses of 
cells with the slightest rubbing against soft wet paper. As soon as 
the seedling develops root hairs, the cap will break up, in this man¬ 
ner and the cap on mature plants is similarly weak. 
Garbondale Peachblow seeds about 
10 years old. Drawing by Ada 
Hayden. 
Figure 6.—The root tip of a 
potato, showing loose cell cap 
at tip. Drawing by Ada Hay¬ 
den. 
