52 
EIGHTH REPORT. 
lular spaces indicate an aquatic habit in the ancestors—not very remote 
■—of the corn. 
Hollow stems, in many of the more rapidly growing herbaceous plants, 
constitute a direct means of aeration of the stem and the more remote 
internal growing structures. 
Submerged plants gain their oxygen and CO, directly from the water, 
and once gained they may be stored up in the intercellular spaces for 
future use. This supply serves a double purpose, namely, to furnish the 
needs of the plant, and to keep it erect in the water. To keep up suf¬ 
ficient buoyancy in sea water requires much less gas content and inter¬ 
cellular space than in fresh water on account of the higher specific 
gravity of sea water. The fact may be easily understood by comparing 
the structure of the tissues of marine plants with those growing in 
fresh water. 
Anerobic respiration ought not to be omitted in any discussion of 
aeration, because it seems to present a contradiction with respect to 
the almost universal need of oxygen in respiration. Anerobes seem to 
gain all the energy they require from chemical action—other than oxida¬ 
tion—within the tissues. One of the resulting products produced by 
some anerobes, is sulphuretted hydrogen, and in this case it appears 
that the chemical action resulting in this compound furnishes energy 
to the plant similar to that furnished by the operation which results 
in the formation of C0 2 But it will depend upon the specific character 
of the organism itself whether it has the power of utilizing the energy 
latent in a given substance. Some maintain that the operation is 
always an oxidation process,—no matter what may be the product 
given out,—that it may be only an end product of which there may be 
a series of two or more, one of which being oxidation, but not carbon 
oxidation. 
In connection with this, a word should be said about intra molecular 
respiration. In the case of many seeds, germination can be carried on 
in the absence of atmospheric oxygen, or pure oxygen; and because CO, 
is liberated by the process, the conclusion is made that oxygen must be 
obtained from the molecules of other substances within the cells. So 
that if young seedlings be deprived of air, they are able to carry on the 
function of respiration to a limited extent. In such respiration, alcohol 
as well as CO, is one of the resulting products. 
Respiration, photosynthesis and transpiration are all involved in the 
process of aeration. Transpiration is usually limited to' mean the 
passage of water—in suspension in the air—from the tissues out to the 
free atmosphere. Roots, stems and leaves are involved in respiration; 
green leaves and green stems in photosynthesis; leaves and stems gen¬ 
erally in transpiration. 
Movement and interchange of gases , are augmented mainly by the fol¬ 
lowing :—change of temperature; diffusion caused by interchange of 
gases; assimilation; transpiration; pressure and the moisture of the 
air; movement of the plant produced by wind or water. 
In some books dealing with botanical matters, the term “breathing” 
is used with respect to interchange of gases, but the term is misleading 
because by inference it involves a comparison with breathing of ani¬ 
mals. They are not comparable because breathing in animals implies 
