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SPONGELET and SPONGIOLE

(diminutives of Sponge). Terms formerly much in use to denote the tips of young rootlets, under the mistaken supposition that they absorbed the plant's food from the soil like a sponge. The formation of new cells in roots goes on (in monocotyledonous plants almost entirely, and in Dicotyledons to effect increase in length) very near the tip, behind the protecting layer, known as the root-cap or pileorhiza. The newly-formed cells are very small; and are so closely packed with protoplasm, as to appear very different from the cells in the older part of the root. The latter cells are larger, and more translucent, containing less protoplasm in proportion to their size. The small size of the cells in the tips of the roots, and their abundant contents, rendered it difficult, with the microscopes formerly in use, to make out the structure of this part. It was supposed that they formed a body like a sponge in its power of sucking in fluid from the soil, and the name Spongiole was, therefore, given. It is now known that the root-hairs, and not the tips of the roots, absorb the fluid nourishment that plants take in from the soil. See Sap.