802 THE POPULAR SCIENCE MONTHLY. 



curious growth, here taking up through the skin and assimilat- 

 ing mineral substances, there producing and transforming or- 

 ganic 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 sun- 

 light, 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 crow- 

 foot, 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 conse- 

 quently 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 resem- 

 bling 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 



