62 RICHARDS AND MAcDovuGAL: INFLUENCE OF 
mens they are swollen to nearly twice their ordinary diameter. 
The bundle-ring of the developing plerome cylinder is scarcely 
greater in diameter in the CO specimens than it is in the normal 
and in the sections examined shows little or no difference in struc- 
ture. Not so, however, in the plants from the gas cultures. Here 
the axial bundle-strand is nearly twice the normal diameter, the size 
of all of the developing bundle-elements is exaggerated to about 
the same extent as is the parenchyma, and the walls are much less 
thickened than they normally are. The difference is very striking. 
The whole stem-base appears to be in a less differentiated condi- 
tion than normal to it at that age, a circumstance which perhaps 
accounts for the very free formation of the extra roots. 
The normal growth being in general checked by the gases 
used, it is natural to suppose that the growth-curvatures would 
also be affected, and such appears to be the case. In CO the seed- 
lings most sensitive (e. g., mustard) showed little or no curva- — 
ture in response to phototropic stimulus, and in gas whatever 
development took place was quite irrespective of the angle of the 
incident rays. Similarly there seemed to be a less degree of sen- 
sibility to geotropic stimulus, especially noticeable in the adven- 
titious roots of the corn and in those supernumerary roots formed 
in the:thickened stem of the same plant. 
Together with the other inhibitive effects of CO and gas it was 
noticed that the chlorophyl formed much less quickly than under 
normal conditions. In fact mustard seedlings, sprouted in the 
dark, scarcely greened after a week’s exposure to sunlight while in 
an atmosphere with gas, though the control showed the effects of © 
the light in the course of a few hours. In CO the action was also 
retarded, but not nearly so much as in gas. It must not be sup- 
posed, however, that this lack of chlorophyl is necessarily the 
explanation of the retarded growth. Most of the seedlings in the 
above described experiments did not in the course of the experiment 
pass beyond the stage where they chiefly rely upon the stored food 
inthe seed. Also in some cases the chlorophy] did finally assume its 
normal color, without bringing about any increase in the rate 0 
growth. Finally it may be said that some experiments which were 
kept in the dark all the time, showed that the etiolated plants behave 
similarly to the ones in the light. 
