362 



A TEXTBOOK OF BOTANY [Ch. VII, 3 



Sometimes they are gigantic in size, as in the Martynia of 



the western plains (Fig. 263). Everybody knows how abun- 

 dantly the weed seeds cling to our 

 clothes after walks in the fields in the 

 autumn; and they cling mostly by 

 hooks. The same result follows from 

 the presence of adhesive coverings to 

 fruits or seeds, as especially common in 

 epiphytes or parasites, for instance, 

 the Mistletoe. In these cases the 

 sticky seeds adhere firmly to the feet 

 of perching birds until brushed off by 

 contact with rough parts of some 

 tree, the adhesiveness then serving to 

 attach the seeds to the tree upon which 

 they must grow. Adhesive seeds occur 

 also in some water plants, which thus 

 become attached to the feet or feathers 

 of wide-ranging water birds, many of 

 which travel so widely as to render 

 those plants cosmopolitan. Thus birds 

 come next after winds and ocean cur- 

 rents as agents of plant dispersal. 



Second, fleshy fruits, with their edible, palatable pulp and 



their bright, contrasting colors, are 



easily found and eaten by animals, 



through the bodies of which the seeds, 



variously protected against injury from 



digestive juices, pass uninjured, and 



thus are dropped far from their places 



of origin. This seems very clearly the 



functional significance of edible colored 



fruits in nature, all lines of evidence 



converging upon this explanation. In 



this way the smaller forms of fleshy fruits, especially the 



diverse forms of berries and the smaller drupes, are scattered 



Fig. 260. — The Coco- 

 nut, in section ; reduced. 



It shows the air-hold- 

 ing husk, the hard shell 

 (black) , endosperm or 

 "meat" (cross-lined), 

 and central cavity con- 

 taining sap, or "milk." 

 Below in the endosperm 

 can be seen the small 

 embryo, which lies just 

 under, and comes out in 

 germination through one 

 of the "eyes." (From Le 

 Maout and Decaisne.) 



Fig. 261. — Head of 

 Burdock fruits ; X \. 

 (From Kerner.) 



