THE LEAF AS A FEEDING ORGAN.

Otago Witness, Issue 2686, 6 September 1905, Page 89

THE LEAF AS A FEEDING ORGAN.

(Continued.)

Last week I should have continued this article from the Education Gazette and Teachers' Aid, but mislaid my copy. Through the courtesy of a teacher who takes this journal I am able to continue the article to-day :: —• The leaf has often been called the lung of the plant. This is based on a serious mistake. Plants breathe exactly as animals breathe They, breathe ia oxygen and biealhe out

caibon dioxide (burnt-up charcoal). There is no dividing line between animals and plants, and, practically cvei> where, breathing consists in taking 111 oxygen, uniting this with the carbon ot the food, thus getting energy to do the work involved in the life processes, and then breathing out the burnt-up stuff, carbon dioxide. Kveiy part ot a plant breathes for itself. With us, on© pait (the lungs) is specialised for breathing, but there is no such specialisation in a plant. Each living plant ceil breathes for itself. So the leaf is not the lung ot the plant. The leaf is a feeding organ. It might be called the kitchen of the plant. The kitchen is the room most watched by boys and girls at home before going to school in the morning. So the leaf is the kitchen. A kitchen is useless without a cook. "Leaf green " is the cook, and a wonderful cook she is. A cook is helpless without a fire. The sun is the fire.

I would like you to look at a leaf. Look at the green. All our food is prepared by this wonderful cook. Take a -simple foodstarch. Man, vdth all his laboratories and appliances, cannot produce simple substances like starch and sugar, substances which, if heated, give only carbon and water; and this is produced at a low temperature, for a high temperature kills the de'icate " leaf green." So the leaf is not only a kitchen, but it is a marvellous chemical laboratory, in which substances are prepared which we cannot prepare.

.Look at this leaf again while we tell its story. " The leaf is the kitchen. ' Leaf green' is tha cook. The jsun is the fire. " Leaf gieen* in sunlight takes the burnt-up charcoal from the air, mixes it with water, etc., irom the root, and forms starch and other foods, wood. etc. At .the same time, the good air* is given out." .Oxygen is a by-product here. The leaf does not need it in feeding, so it is got rid of.

in the last lesson we started with charcoal in the form of food, fuel, etc., and mixed it with good air (oxygen). r lhe charcoal disappeared apparently; but really we found we had an invisible gas, " burnt-up charcoal " (carbon dioxide). This floats about in the air, leaf green takes it, unites it with water, etc., and lornis food, etc., giving back the good air.

Animals take food ready made, mix it with 0 and give out 002. The plant in feeding takes CO2 (burnt-up charcoal}, causes the O to unite with water, etc., irom the root, and forms starch, etc., and gives out O, but not in breathing.

In feeding, we eat ready prepared food. The plant takes the simplest compounds ai.d nianufactuies them up into complex ones. Except with a very few plants, which have a colouring matter closely allied to " leaf green,'' only green plants can do this. Mushrooms (fungi) have to live on food already prepared.

You will readily see now what gave rise to the old saying that it was healthy to have plants in the room in the daytime; but inheaithy to have them there at night. At night they breathe as we breathe, and so use up air. Of course, they do not need as much energy as" we need, and so do not breathe nearly so vigorously. In the daytime they take in about 30 times more carbon dioxide than they breathe out, so the breathing has no harmful efiect. " To show t^-;t oxygen is set free, take some watercress or the long green " frog's blanket," put it under, a glass funnel in a glass jar full' of water. Over the end of the funnel invert a test tubs full of water. Soon bubbles of gas rise. This gas causes a glowing splinter to burst into' flame—it is oxygen. :