How Plants Secure Change of Location 393 



5. Flotage upon Water. When water moves onward in currents, 

 whether merely those minor and temporary kinds made by winds 

 in their sweep over lakes, and by rains in the rivulets they cause, 

 or in the mighty and permanent streams of river and ocean, it 

 forms a good agency of transport even though less widely useful 

 than winds. 



With water-currents, as with others of the methods, some 

 transport is incidental, as when floods tear out whole plants from 

 the banks and leave them to grow anew in another location when 

 the waters subside, or as happens when rivers sweep broken 

 twigs of Willow to new places where they readily strike root. 

 Again, rain drops splash out from open capsules, spores or small 

 seeds which are carried away in rivulets to places where they are 

 left in dampness good for their germination. Thus also are 

 carried little buds (gemmae) of the Liverworts, and probably the 

 axillary bulblets produced by several kinds of plants. Besides, 

 most wind-scattered seeds are so light that they float well upon 

 water, and thus effect a still wider transportation. But these in- 

 cidental methods are insignificant in comparison with those which 

 are secured by adaptation in the plants. 



In the first place, some kinds secure transport by water-currents 

 through their very habit of life, which indeed may be partly de- 

 termined to this end. Such are the 

 free-living submerged Algae, which in- 

 clude vast numbers of the simpler 

 kinds of Seaweeds, and the free-float- 

 ing plants like our Duckweeds (figure 

 163) and the Water Hyacinth, with FIG 163 _ The Duckwe ed, a float- 

 similar kinds of the tropics. And a in g P lant - (Copied from the 



. . Chicago Textbook.) 



modification of this habit is found 



in some sorts of our own, like some Watercresses, which are only 

 lightly attached and are readily moved to new places; while many 

 kinds of our water-weeds form naturally-detachable buds which 

 are easily floated afar. 



