1905] SNOW—DEVELOPMENT OF ROOT HAIRS 21 
JAR 2. 
GROWTH IN 24 HRS. |Gpowrn PER HR. (mm.) 
(mm.) 
24-HR. PERIODS Temp. ConDITION 
Water | Air Water Air 
LG 8 4. Say 5 0.63 oot 12° | Few towards top 
1 (age eer ger ah 6 Sat 0.25 It No hairs 
JE 8 Pere . 7 fe 0.29 scales 14 | No hairs 
UN acne sous 10 ie 0.42 19 | Hairs ise to last air 
Mises ee 15 ff, 0.63 srt 18 | No hai 
Vises ose ce 5 10 0.84 0.42 18 Abundant i in air, none 
WIE Saya 15 i. 0.54 ests 12 Little. pon le at top 
Vitis See cee To “potig 0.42 18 Abundant 
LAS eae Rais 6 ae OF25 el ee Good hairs 
Average....- 12.5 8.4 0.52 0.35 
x) j ) 
An attempt was made to ascertain whether the difference in rate 
of growth of corn seedlings in air ani water could be the cause for 
the lack of root hairs in the latter medium. The seeds were planted 
in sniall pots in a mixture of sand and humus, or in garden soil, and 
the roots allowed to pass through the bottom of the pots. By placing 
the pots in the tops of wide-mouthed bottles half full of water, the 
roots hung in moist air, and by changing the level of the water, 
alternating conditions of air and water were brought about. The 
roots were allowed to remain in each medium for twenty-four hours. 
It will be seen upon examination of the above tables that there 
‘was a general tendency to produce hairs’ in air and to cease their 
development in water. The effect of the air was not lost imme- 
diately, but in some cases the hairs extended a short distance into 
the water. I see no satisfactory explanation for the non-appearance 
of hairs in the first air measurement in jar 2. Lack of energy from 
low temperature appears to be the most simple explanation. The 
short growth in the following water period was still in the elongation 
phase when placed in air, and hairs are developed by differential 
elongation. Other experiments not recorded here gave the same gen- 
eral results. s 
4 Grew into water and the different rates could not be calculated; so that as two 
air periods of 10™™ growth had a rate of ©.42™™ per hr., that was'assum 
calculation. 
5 Measurements of a rost at the top of the jar. 
