tains, 
Oe) em el te Ramen Pet =e ae oe ea. 
1905] SNOW—DEVELOPMENT OF ROOT HAIRS 23 
placed under a smooth straight root, but in twenty-four hours the 
root had curved and grown past the surface, a tuft of hairs on the 
curve indicating that some retardation of growth took place. For 
over a week the curling and hair production continued, then the root 
grew horizontally and struck the glass side. It became kinky and 
hairs continued to be formed for five days. 
/ The fact that kinking takes place in free water 
— shows that some other factor or factors besides 
= resistance must be acting, but the facts brought 
out in the two experiments make it appear possible 
that resistance may be a partial cause for the 
kinking and hairiness of roots. 
As the plaster cup in the preceding experiment 
was unsuccessful, glass tubes were tried. They 
were of sufficiently small bore 
to prevent a relief of pressure 
by too great bending. Smooth 
roots of corn were repeatedly 
Fic. 11.—Diagram allowed to grow into glass 
of apparatus to stop tubes (fig. 12). Usually the 
the growth of a root tin became more or less 
by a glass rod. ° ‘ 
swollen, nearly or quite filling 
the tube. Primary roots showed kinking at the 
bottom, and hairs appeared in diminishing 
lengths from the bottom to the top. Only a few 
hairs appeared on the adventitious roots. When 
kept at high temperatures (24-34°C) the roots 
grew smooth, although bent and curved. If 
the resistance were relieved by allowing the roots | 
to curve above the tube, hairs ceased to appear, Vis 1s one 
conforming with the statement of MER (51, p. of apparatus to stop 
584) that feeble retardation is not able to produce the growth of a root 
hairs. In one experiment the growth appeared >Y * £!88s tube. 
to be so great that the roots were crushed and broken, producing 
no hairs on these portions. 
a 
