Page:Popular Science Monthly Volume 47.djvu/820

802 curious growth, here taking up through the skin and assimilating mineral substances, there producing and transforming organic matter, and at the same time advancing the growth and increase of the whole. Not less peculiar than the inner structure and appearance of the stem is the form of the leaves of water plants. Their service to the organism is the same with that of the leaves of other plants. They supply, with the help of the sunlight, matter which the plant needs for building up its body. The conditions under water are not very favorable for this work, for the rays of light suffer considerable loss of intensity in passing through even a thin sheet of water. In connection with this there are leaves growing under the water, as in the floating crowfoot, as a rule not flat or oval or cordate or round, like most other kinds of leaves, but divided into the thinnest threadlike strips, which, with the largest surface development, obstruct the least possible light from one another and easily yield to the current.

The leaves that are destined to live on top of the water are otherwise constructed. They will not overshadow one another, and they are exposed to the full light of the sun. They need only to receive it on as broad a surface as possible, and so to float that the weight of the food-stuff accumulated within them all the day long shall not cause them to be submerged. These leaves consequently do not present divisions or ramifications like the leaves of roses and acacias. They form reniform or oval disks, which lie flat upon the water. Every one will recollect this who has seen the yellow and the white pond lilies. The brownish spawn weed and the beautiful white flowing frog spittle likewise have swimming leaves; and there is a marsh crowfoot which has these and submerged threaded leaves all on the same stalk. In the duckweeds stem and leaf are not distinguished, and the plant is only a flat disk with a few insignificant rootlets on the under side; and in one species these are wanting. The plant is only a little floating leaf, with a pocket for the reception of the scantily endowed flowers.

The floating leaves of the Victoria Regia are beautifully developed. They have the form of flat plates with a narrow, upturned border—a form more favorable to their notation. The green leaves, a yard or more across, with the pink flowers resembling gigantic lilies scattered among them, present a remarkable spectacle.

One of the most remarkable peculiarities of the floating leaves of our water plants is that they never grow up above the surface of the water. The plant appears to know when that point is reached. As we shrink from sudden contact with cold water, these leafstalks suspend their growth on contact with the air. They grow just long enough for the leaf expansion to reach the