March, 1922] 
TELLEFSEN — 
RELATION OF AGE TO SIZE 
123 
on window sills supplied with bottom heat from radiators. The water in 
the jars was renewed as needed and entirely changed about once a month. 
Benedict (191 5) in writing of senile changes in physiological activities 
of plants says that "the most obvious characteristic is a decrease in rate of 
growth." McFarland mentions in a recent test that the regenerative power 
appears to be greater in proportion to the youth of an animal. The present 
writer found that cuttings from younger trees rooted in less time than those 
from older trees. Leaves appeared on cuttings of younger trees before they 
did on those of older trees. 
When roots appeared on the cuttings, they were allowed to grow until 
about 2 J to 3 inches long. Then sections were cut from roots of the several 
cuttings 2 inches back from the root tip and put into Flemming's strong 
solution. The sections were taken 2 inches back from the root tip in order 
to find differentiation of the ground meristem. 
After the usual killing, washing, and dehydration, the pieces of roots 
were imbedded in paraffin, and both longitudinal and cross sections were 
cut six microns in thickness. The sections were stained in safranin and 
Mayer's haemalum, or in safranin and light green. After being stained, 
the sections were mounted in balsam. 
Measurement of Root Cells 
When the prepared root sections were examined, it was found that large 
air spaces had developed in the cortical tissue. The number of these air 
spaces was found not to be constant, but varying from three to five, four 
being the common number. This provision for aeration gave the cross 
sections a decided three-, four-, or five-rayed appearance, the number of 
xylem strands coinciding in each case with the 
number of large air spaces. 
Somewhat similar conditions have been re- 
ported for other plants. In 1888 Scott and 
Wager recorded the fact that the primary cortex 
of floating roots of Sesbania aculeata Pers. con- 
sists of rounded cells among which are very large 
lacunae filled with air. 
Lily Batten (1918) mentions the fact that cor- 
tical root cells of Epilohium hirsutum are very 
loosely packed in young roots and that large 
air spaces occur in the roots of plants grown Fig. i. Cross section of 
under very moist conditions. ^^^^ of -^^^^"^ ^^^^^ Marsh., 
Ada Hayden (1919) found cortical air spaces ^ho-.ing three large air spaces 
... 1 and a three-rayed condition 
m roots of prairie plants studied. of the cortex, x 90. 
In 1 91 3, Norris planted Zea Mays in various 
media and examined the structure of the roots. He found that the medium 
used influenced root structure, particularly that of the cortex. Air spaces 
