800 THE POPULAR SCIENCE MONTHLY. 



element. The doctrine of the Greek philosophers, that every- 

 thing is derived from water, is so far correct for the vegetable 

 world that the first plants that appeared on the earth were water 

 plants. There were probably little microscopic forms inhabiting 

 the barely cooled waters of the primitive seas before there was 

 any land to afford a suitable home for any living beings form- 

 less albuminous masses, like " organisms without organs," which, 

 like some of the bacteria, drew their food from the dead stone. 

 Like their living kindred, the lower AJgce, they were of too tender 

 nature to be preserved in the cavities of the sea slime. The first 

 remains seemingly of vegetable character preserved in the oldest 

 strata of the earth's crust are therefore of relatively large fucoids. 

 Their existence justifies our supposing an already richly devel- 

 oped flora of Algce- such as is now found in the deepest parts of 

 our lakes. Mosses, ferns, and flowering plants are absent. They 

 appear later, and under conditions which prove that they were 

 produced not in the sea but on swampy land. Geological evidence 

 shows us that only the Algce, and the fucoids originated in water 

 and were water plants from the first. The other water plants, 

 especially flowering plants growing in water, were driven into the 

 water by increasing competition among the growing number and 

 variety of the land plants, and assumed the properties that now 

 distinguish them from land plants during their compulsory emi- 

 gration, and in consequence of their water life. This process is 

 now going on in our sight in a certain plant the wandering knot- 

 grass a relative of the small-flowered, spreading swine grass and 

 of the adderwort. This plant grows on the borders of ditches 

 and ponds, often half on land and half in the water ; and it can 

 not escape the attentive observer that it presents a quite different 

 appearance in the water from that upon land. Stiffly haired, and 

 having short-stemmed leaves on land, it is in water bald and 

 smooth, and develops very long leafstalks which terminate on 

 the surface in flat, floating expansions. Here there is a plant 

 which only occasionally, and usually only partly, makes its home 

 in the water, and is in a position to suffer such remarkable 

 changes that it is no longer a wonder that plants which have be- 

 come entirely at home in the water are very little like those of 

 their genus which remain land plants. Of many of them, in fact, 

 it can no longer be determined from what family of land plants 

 they are really derived. Even such well-defined plants as sea- 

 weed and duckweed would not at first sight suggest to any one 

 relationship with the Arum family. So with the water crowfoot, 

 which we shall take as our starting point in the discussion of the 

 properties of water plants. Well known are its little white flow- 

 ers, which adorn the ponds and even the swift streams in the 

 summer time. 



