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To make this statement clear and to show why I lay such emphasis
on an apparently obscure point, which, however, I believe to do the key to the fertility problem, let me recall the fact presented to us by the physiologists concerning the development of a root and we will find the wonderful provision that the plant seeks the water rather than the water being moved by the soil to the plant. The root of a plant is absorbent for mineral matter only at the tip and for a very short distance back frcm the tip only a small fraction of an inch. It is something like one-tenth of an inch of the root that actually absorbs water and mineral food. This portion of the root is only absorbent for a few days, probably for not more than three or four days. As the tip is extended into new fields of moisture and plant food, the part that was absorbent yesterday ceases to be absorbent to-day. There is therefore no reason why water should move up to the plant from any considerable distance, for the plant itself constantly moves its feeding roots out into new field. Mr. "Walker. That applies to all plant growth? Professor "Whitney. Yes it applies to all cultivated crops. These are interesting points which I tell you, not simply because they are scientific interest, but because I think if I can get you to see the soil as I do, to look into the soil and the economy of the plant and its habits of growth, you can grasp some of the problems in soil fertility that we have heretofore found most difficult. There is another interesting provision in the drinking of plants, which is that after this root tip has progressed, after it c-aj^s to become absorbed, ceases to be of use in taking up food and drink for the plant, it imme diately corks over it puts on a hard layer of cork cells, large cells called "balloon cells," full of air, to prohibit the further entrance of water or other material from the outside into the roots. The reason for this(if we can speak of the laws of nature in this way), or the result of this, is to prevent certain substances thrown off bv the plant from reentering its tissues the plant protects itself against its own effluvia. And here we see the importance of the absorptive power of the soil, which permits it to seize and hold with great tenacity organic matters given off by the roots and prevents the active circulation of water containing the excreta of plants except in dilute solutions following rains. This I shall speak of again when I dis cuss the sanitary environment. (This Article to be continued in the May issue of the Light.) 14.