THE LIFE OF WATER PLANTS. 801 



These little blossoms, thickly massed on the surface of the 

 water, or sitting on long stems, spread out their five petals, which, 

 with their numerous stamens and styles, mark them as relatives 

 of the buttercups. In the other parts we look vainly for resem- 

 blances with the ranunculuses. If, for instance, we take one of 

 them which we find floating in running water, out of its element, 

 the whole plant falls together, and we hold in our hand nothing 

 but a bunch of long threads, in which no difference can be per- 

 ceived between stems and leaves. If we spread a part of the 

 bunch upon a stone, we may discover branching shoots beset with 

 leaf forms; but both organs are widely different from those of 

 their nearest generic relatives. The stems of the ranunculuses of 

 the fields are upright, stiff, skeletonlike, strong enough to defy 

 wind and storm, and able to bear the weight of their leaves, 

 flowers, and fruits. The stems of the water ranunculuses are 

 slack and weak. They are swung around helplessly by the waves, 

 winding hither and thither in the direction toward which the run 

 of the stream carries them. They are stable only in the direction 

 of their length, because in any other case the current would carry 

 them away. In other respects the stem does need cohesive power. 

 The whole plant is pierced with connected air passages, and all 

 its parts are adapted to floating or swimming. The water here 

 takes the burden upon itself which is imposed on the stems of 

 land plants. Floating plants need no skeletons; and dissection 

 and microscopic examination show that all those forms are want- 

 ing in their interiors which, like the bones of animals, give sta- 

 bility and tenacity to their structure. 



Many water plants lack organs still more closely associated 

 with the life processes. We can not conceive of a higher animal 

 without veins and lymph-vessels. But in water plants we not 

 seldom miss the long and broad ducts of which the vascular sys- 

 tem of land plants is constituted. At all events the vessels do 

 not perform so important a part in the vegetable kingdom as the 

 circulation of the life juices in the animal kingdom. Their prin- 

 cipal service is to carry water from the roots to the leaves. From 

 this we can understand how organs essential to the life of land 

 plants can be dispensed with in water plants. They do not need 

 a special conducting of water, because they are surrounded by 

 that element on every side. The most marked instance of the 

 absence of internal organs is met in an alga which forms green 

 fields in the deeper parts of the Mediterranean Sea. It has slender, 

 branching, horizontally creeping stems which develop above in 

 the water into leaves and below in the sand into fine thread roots. 

 But the whole plant, often many feet in length, consists only of 

 single gigantic cells. A tough skin incloses its juices, which flow 

 in a continuous stream through the stem, leaves, and roots of the 



VOL. XLVII. 65 



