940 



THE NATURE BOOK 



a native, spreads amazingly by means of 

 its seeds ; these are encased in a capsule 

 which readily floats. On the Loddon, a 

 tributary of the Thames, the species has 

 spread up and down the stream amazingly, 

 and it is gradually extending to the main 



J J .. . 



/NCH£:s 



THE SEED CASES OF THE MARTYNIA. 



stream. As years go by it is hkely that 

 the Snowflake will become increasingly 

 plentiful, until it is distributed throughout 

 the Thames water-system. An astonish- 

 ing illustration of the distribution of a 

 plant by water is that afforded by the 

 American water-weed Elodea Canadensis, 

 a species which somehow was introduced 

 into Britain about sixty years ago. In 

 this short while it has managed to spread 

 over most of the water-ways of Great 

 Britain. Indeed, in many districts the 

 plant has blocked canals to such an extent 

 that it has prcn-ed a real hindrance to 

 navigation. 



The number of seeds whii h arc dis- 



tributed by animal agency is immense. 

 All kinds of devices are adopted to secure 

 the conveyance of the seed from its parent 

 to a distant situation where it wiU stand 

 a reasonable chance of securing room for 

 de\'elopment. Those seeds having hooked 

 vessels exhibit a variety of 

 method which is amazing. Some, 

 like the Martynias of .\merica, 

 are provided with hooks many 

 inches in length ; these seize 

 hold of any passmg animal as it 

 plunges through the forest, be- 

 coming deeply embedded in the 

 flesh, and the victim will per- 

 haps travel several miles before 

 it can divest itself of its painful 

 burden. Even more formidable 

 still is the seed vessel of the 

 South African Grapple Plant 

 {Harpagophyton procumhens). 

 These roll about over the dry 

 plains, and as they are provided 

 with a large number of curved 

 hooks, readily attach themselves 

 to the coats of animals. Indeed, 

 it is said that they have even 

 been known to cause the death 

 of hons. Finding some of the 

 seeds attached to its skin, the 

 animal endeavours to tear the 

 cruel hooks away, with the re- 

 sult that it gets one of the 

 vessels hopelessly entangled in 

 its mouth, and so perishes in a 

 most miserable fashion. 



Many of our British plants 

 produce seeds provided with 

 hooks, although these are no- 

 thing like as formidable as the 

 two foreign species described above. In- 

 deed, the seed vessels of the Agrimony, 

 the Cleavers, and the Burdock are really 

 objects of great beauty. That the pro- 

 cesses serve their purpose admirably is 

 well known to anybody who has taken a 

 walk in a field at seeding time. One's 

 garments become quite thickly covered 

 with the seeds, which hold on with great 

 tenacity. From this it is easy to get an 

 idea of the distance to which many of 

 these may be carried whilst chnging to 

 the coat of some wild creature. 



A ver\' large number of plants are able 

 to surround their seeds with a pulp which 

 is attractively flavoured. It is certainly 



