Nov. 1, 1901. ] Supplement to the " Tropical Agriculturist." 
363 
PLANT LIFE. 
[a series of simple lectuees intended 
eos a class of juniok students.] 
LECTURE II. 
Eespiration or Breathing. — In hiimaii beings 
respiration consistb as you krow of breathing in 
and out, and you no doubt further know that 
•what is breathed in is "pure air," and Mhat is 
breathed out "impure air." Row the essential 
difference between these two is that the former 
consists almost entirely of a gas called oxygen and 
the latter of a gas kcowu as carbonic ncid. At 
present I do not mean to go fully into the nature 
and properti:;s of these gases as taught us by che- 
mistry, but in order that you may correctly un- 
derstand the process of respiration, I must tell you 
one or two facts about them. The air which we 
breathe consists of a mixture of two gases called 
oxygen and nitrogen. It is the oxygen of the air 
which is the essential element for the purpose of 
respiration, though in breathing we take in 
both gases. Chemists tell us that nitrogen exists 
in the atmospheie as a dilutent of the oxygen, 
as pure oxygen is, so to speak, too strong and by 
itself is unsuitable for human respiration, just 
as certain medicines cannot be taken without 
reducing their strength by the addition of water. 
As the derivation of the word signifies, oxygen 
is the " life giver," aud when a person is suffo- 
cated for want of air, it is the absence of 
oxygen which causes the loss of life. The chief 
function of the oxygen which is breathed in may 
be said to purge the blood of the waste matters 
which occur in it as the result of wear and 
tear. Now the element which predominates in 
the human body (as well as in the plant) is 
carbon, and hence carbon is the chief waste 
material found in the blood. It is removed by 
oxygen combining with it and carrying it away 
in the combined form of carbonic acid, the 
compound of carbon and oxygen which is found 
in the expired breath. This carbonic acid is 
in any appreciable quantity hurtful to man, 
that is it is poisonous. Hence the necessity 
of well-ventilated dwellings. You know how 
uncomfortable any one feels in a crowded room in 
which many people are breathing out carbonic 
acid and there is no free current of air. As a 
rule his head aches and he begins to feel sick 
under such circumstances, while some people faint 
off. These are all indications of the presence of 
too much carbonic acid in the air. If you have 
read Indian History you will recall to mind the 
incident of the Black Hole at Calcutta where a 
Dumber of English soldiers were crowded into 
a small room and left to be suffocated. In clean- 
ing old and abandoned wells people have to be 
careful that there is not a collection of carbonic 
acid at the bottom which will suffocate them. 
The gas being heavier than air has a tendency 
to remain at the bottom of wells and tan pits in 
which organic matter has been left to decompose. 
Under such ciicumstances it is safe to first employ 
some means for disturbing the gas and mixing 
it with ordinary air, and one way that this is 
done is by letting down a bundle of straw by a 
rope and moving it up and down frequently till 
the gas has been sufficiently mixed with air to 
render it less harmful than it would otherwise be. 
Some people think that if a lighted lamp which 
is lowered into the well does not go out, it is safe 
for a man to venture, but though a light may burn 
in it, the air in the well or pit would still be 
dangerous for a person to breathe. For the present 
1 think I have told you quite enough about oxygen 
and carbonic acid, but later on I mean tO'show 
you in a practical way something of the properties 
and behaviour of these gases that would interest 
you more than the mere description I have given 
you. 
Now the process of respiration in plants 
is practically the same as that of animals, 
for in breathing plants take in oxygen and give 
out carbonic acid just as animals do. You might 
well ask how is it, if all plants and animals take 
in oxygen and give out carbonic acid that the 
atmosphere does not become poisoned, so to 
speak, by the exhaustion of the oxygen of the 
air, and the increase of the carbonic acid. Well 
this is prevented by a provision of nature where- 
by the composition of the atmosphere is practi- 
cally the same at all times. But I will not make 
any further explanation as regards this matter, 
because 1 shall have to refer to it more fully 
under the subject of nutrition. 
There is another point I might refer to in order to 
explain the importance of respiration, namely, the 
maintaining of the internal heat of the organistn, 
for the combination of oxygen with carbon pro- 
duce a certain amount of heat which is necessary 
for a healthy condition. The machinery for res- 
piration is, of course, not the same in plants and 
animals, no more than it is the same in different 
animals such as man, fish, insects and so on. You 
would no doubt like to know by what means 
plants take in oxygen and give out carbonic acid, 
or how gases pass in and out. In our case the 
mouth is the external opening through which res- 
piration takes place. Well, the plant too may be 
said to have a mouth or rather several mouths. On 
the leaves, and particularly on the under surface 
of ordinary leaves, are openings called stomata 
(each being culled a stoma which in Greek signi- 
fies a mouth.) These openings are guarded by 
two more or less curved cells which we may 
compare to our lips. It is through these stomata 
that respiration in plants takes place. They 
are so small that we cannot see them with the 
naked eye, but we can do so bj^ the aid of the 
microscope, and I will close my lecture to you 
to-day by shewing you these minute mouths 
through that instrument. There are other duties 
required, of these stomata which I shall tell yon 
about later on in another connection, 
C. D. 
♦ 
DIPEEEENT SYSTEMS OF HOUSING CATTLE 
AND COis^SERVlNG MANURE. 
[report by the PRINCIPAL, CAWNPORE 
AGRICULTURAL SCHOOL.] 
At the Cawnpore Experiment Station this sub- 
ject has been under experiment and observation 
during the past five or six years, and the object 
