392s dd. C. Draper—Evolution of Structure in Seedlings. 
same, and we lengthen the resonator tube $ meter, the serrated 
flames of the resonator will be displaced } of the distance be- 
tween the centers of two contiguous serrations ; : 
be lengthened 1 meter, or one wave-length, the displacement will 
amount to the entire distance separating the centers of two 
contiguous serrations; and for n number of wave-lengths of 
elongation of tube, we shall have n number of such displace- 
ments. Thus can be measured a wave-length; and if the 
number of vibrations given by the pipe be accurately known, 
we can reach with the manometric micrometer an accurate 
determination of the velocity of sound. 
Finally, we are bold enough to believe that we have in the 
highest development of the method, a means of tracking 1 
the air the resultant wave-surface of combined notes; and, 2 
short, of bringing the exploration of acoustic space to approach 
somewhat to that precision of measurement which, for over 
half a century, has characterized the study of the eethereal 
vibrations producing light. 
September 21st, 1872. 
Art. XLVL—Growth or Evolution of Structure in Seedlings ; bY 
JOHN C. Draper, M.D. 
THE continuous absorption of oxygen, and formation of car- 
bonic acid, is an essential condition of evolution of structure, 
both in plants and in animals. : tl 
The above proposition in so far as it relates to es bis 
robably be admitted by all; the opposite opinion is, however, 
Pp y § ’ PP p to show that 
in these organisms, as in animals, growth as applied to evolu- 
e discussion of the proposition in question nec 
involves a preliminary review of the character of oe gases 
: : i. 
that they change their action according as they are examin die 
in the a ee or in the dark, exhaling oxygen under the first con®” 
tion, and carbonic acid under the second. Various explan® 
tions of this, change of action have been given, that generally 
- accepted accounting for it on the hypothesis of the absorptio® 
