260 



A TEXT-BOOK OF BOTANY 



certain plants belonging to an adjacent continent may 



often be explained in this way. 



154. Dispersal by animals. Only a few illustrations 



of this very large subject can be given. Water-birds are 

 great carriers of seeds, which are con- 

 tained in the mud clinging to their feet 

 and legs. This mud from the borders of 

 ponds is usually completely filled with 

 seeds of various plants. One has no con- 

 ception of the number until it is actually 

 computed. The following extract from 

 Darwin's Origin of Species illustrates this 

 point : 



"I took, in February, three tablespoonfuls of 

 mud from three different points beneath the water, 

 on the edge of a little pond. 

 The mud when dried weighed 

 FIG 257. Akene only 6 1 ounces; I kept it cov- 

 of Spanish nee- ere d up i n m y study for six 

 dies with barbed 



appendages.-Af- weeks > pulling up and counting 



ter KEENER. each plant as it grew; the plants 



were of many kinds, and were 



altogether 537 in number; and yet the viscid mud 



was all contained in a breakfast cup!" 



Water-birds are generally high and 

 strong fliers, and the seeds may be trans- 

 ported thus to the margins of distant 

 ponds and lakes, and so become very 

 widely dispersed. 



In many cases seeds or fruits or heads 

 develop grappling appendages of various 

 kinds, forming the various burs, which barbed appendages. 

 lay hold of animals brushing past; and 

 so the seeds are dispersed. Common illustrations of 

 fruits with grappling appendages are Spanish needles 



