386 BOTANICAL GAZETTE IMAY 
that, furnished with sufficient quantities of these materials in the 
proper proportions, a root would continue to grow indefinitely. 
The excised roots of corn, however, will not grow indefinitely 
under the conditions described. Their development is rather 
definitely limited in the dark in the culture solutions used, as can 
be noted from the following experiment. 
Root tips of corn were grown in the dark in the Pfeffer’s solution 
containing 2 per cent glucose. At the end of eight days the tips 
of the roots were cut off and transferred to a fresh solution of the 
same composition, where they were allowed to grow for ten days. 
At the end of that time the tip was again cut off and transferred to 
a new solution. Growth took place there for ten days. If the 
nutrient solution were complete and no inhibiting or injurious 
factors active, by continued transfers we should be able to keep a 
root tip growing indefinitely in the same way as cultures of bacteria, 
molds, or yeasts are kept growing indefinitely by continued transfers 
to fresh media. 
In this experiment the growth during the first period was excel- 
lent, and the number of secondary roots large (table V). During 
TABLE V 
GRowTH OF ROOT TIPS OF CORN IN NUTRIENT SOLUTIONS: ROOT TIPS IN GLUCOSE 
SOLUTION CUT OFF AND TRANSFERRED AS INDICATED 
Aileen <i 
> ret 
0 ina 
ne roots per root 
length (cm.) 
: Number Gain in 
Period of _ ots uaed length (cm.) 
Pfeffer’s solution plus 2 per cent glucose 
es 
June 3o-July 7............ 16 3-43 8.98 64.8 
Fuly P-JULy 19 60.5 ke ee 16 3.48 2.04 20.8 
daly rp-Jaly 28... 2... 13 1.86 0.14 00.90 
: Pfeffer’s solution 
June 30-July 28........... 10 3.65 0.90 | 00.0 
the second period the increase in length was one-fourth that of the 
first period, and the number of secondary roots one-third. In 
the third period hardly any increase in length was found, and no 
secondary roots were produced. 
