198 LIFE : OUTLINES OF GENERAL BIOLOGY 



{Impaiiens noli-me-tangere) refers to its ready explosiveness. At a 

 touch the ripe valves roll up like springs and send the seeds flying; 

 but the force in this case is due to turgid living cells in the walls of 

 the fruit. The extreme case is the Sandbox Tree {Hura crepitans), 

 where the drying fruit explodes with a noise like a pistol-shot and 

 shoots the seeds for a few yards. Explosive fruits are not necessarily 

 dry, for the squirting cucumber of the Mediterranean first frees itself 

 by internal osmotic pressure from its stalk, and then forces out the 

 fluid contents and the seeds through the hole thus formed. In connec- 

 tion with parasites we have mentioned the unique Califomian 

 mistletoi'. which may shoot its seeds for several yards on to an 

 adjacent branch. 



(4) Miuiy fruits are covered externally with hooks or roughnesses 

 which cause them to adhere to passing animals, as is well illustrated 

 in burdock, cleavers, medic, hound's-tongue, and cockle-bur. After 

 a time the external passengers fall off, it may be miles from the place 

 wlure they became entangled. Darwin called attention to a frequent 

 variation of this method, when birds carry seeds in the mud-balls 

 which are formed on their feet or shanks. Let us cite his most 

 famous casi', discussed in the Origin of Species (1859). "Prof. Newton 

 sent me the leg of a red-legged partridge (Caccabis ruja), which had 

 btt-n woundrd and could not fly, with a ball of hard earth adhering 

 to it, luid weighing six and a half ounces. The earth had been kept 

 for three years, but when broken, watered, and placed under a 

 glass, no less than eighty-two plants sprang from it: these consisted 

 of twelve monocotyledons, including the common oat, and at least 

 one kind of gniss, and of seventy dicotyledons, which consisted, 

 judging from the young leaves, of at least three distinct species. 

 With such facts before us, can we doubt that the many birds which 

 are annually bhnvn by gales across great spaces of ocean, and which 

 annually migrate— for instance, the millions of quails across the 

 Mediterranean — must occasionally transport a few seeds embedded 

 in dirt adhering to their feet or beaks?" 



The last word suggests the peculiar case of the mistletoe and the 

 missel-thrush referred to in another connection. For while the missel- 

 thrush often succeeds in swallowing the glutinous berry outright, 

 and may void the undigested .seed on some distant tree, what we 

 are sure of is that the ordinary planting of the mistletoe occurs when 

 the missel- thrush wipes from its beak a seed enclosed in the viscid 

 pulp which it has failed to .swallow. 



(5) A .somewhat jiaradoxical way of .securing dispersal is to be 

 swallowed by bird or beast, the success depending on the fact that 

 the seed may be ejected from the mouth or the crop, or may be 

 voided from the fcxxl-canal before digestion has occurred. In this 

 way the seeds of some of the stone-fruits and many of the berries 

 are scattered. In this connection there may be some advantage in 



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