MICHIGAN ACADEMY OF SCIENCE. 
51 
leaf be immersed in water, it is equivalent to depriving it of oxygen. 
Aaerial leaves will not live under such conditions. The farmer knows 
that if his winter wheat be covered over with water or ice, for any length 
of time, the crop is destroyed. The destruction is mainly due to the 
fact that the supply of oxygen is cut off. If a pool of water lie on a 
grain held so as to submerge the crop for some time, the plants are 
killed. In the winter time vital activity in the wheat is very slow, con¬ 
sequently the plants would not die as quickly as they would if sub¬ 
merged in summer. Winter wheat may remain alive under snow be¬ 
cause there is enough air in the snow to supply all the needs. Snow 
does not shut off the air supply, and if the plants be wholly dormant 
they may survive for months without air, but winter wheat is not wholly 
dormant, even when growth seems to be stopped. 
The aerating system of stems of corn, sugar-cane, bamboo and the 
like, is a special one. These have no lenticels. As the stem of corn 
(for example) increases in diameter, new flbro-vascular-strands are 
formed, and new tissue is developed near the surface, causing the epi¬ 
dermal cells to separate, here and there, and sub-epidermal cells are 
forced out to the surface. Through these young cells, aeration takes 
place. These epidermal cells which are forced out soon become lignified 
and thick walled like the others, especially on the outer side; and were 
it not for the fact that new cells were continually pushed to the sur¬ 
face, aeration could not take place in the stem. In a cross section of a 
stem of corn, it can be seen that here and there on the surface are a 
few cells—-two or three—which are thin-walled as compared with the 
regular epidermal cells. It is through these thin-walled cells that aera¬ 
tion takes place. This method of growth is not only a provision for 
enlargement of circumference of the stem, therefore, but also a provi¬ 
sion for aerating the growing tissue. The surface of the stem never 
becomes rough as it does with dicots, for the outside layer is composed 
of cells which are touching one another. They are not loose as they 
are in the body of the lentieel of dicots. The air must pass in through 
the Avails and not between the cells, and as a general rule where oxygen 
may pass in, carbon dioxide may pass out. 
Water plants and marsh plants have an internal air system of their 
own. This consists of a system of intercellular spaces running length¬ 
wise with the stems or leaves, and occupying the greater part of the 
plant body. The submerged parts are not provided with stomata, but 
interchange of gases is maintained by the internal atmosphere within 
the large spaces just mentioned. This internal atmosphere is replen¬ 
ished by the diffusion Avhich takes place in connection with the sur¬ 
rounding atmosphere. In marsh plants, such as rushes and sedges, 
Avhich stand partly in the water, the large vertical intercellular spaces 
form connecting channels through which the atmospheric oxygen, with¬ 
out being exhausted, can reach the organs growing deep in the mud 
surrounded by marsh gas, and othercvise cut off from any communica¬ 
tion with the air. 
In corn and many other monocots, there is a comparatively large in¬ 
tercellular space within the mature fibro-vaseular-bundle. This inter¬ 
cellular space runs the whole length of the bundle and is quite analagous 
to the air spaces in aquatics and semi-aquatics. In fact these intercel- 
