24 Origin of the British Flora. 



animals, and part of which is cut off by a fence so that it 

 has remained undisturbed. Umbelliferous plants which 

 possess burrs, however, behave quite differently. They are 

 less tall and springy, and, like other plants with burrs, are 

 so arranged as to scrape the burrs against any passing 

 animal, but usually not to fling them. 



Many plants have capsules so arranged as to scatter the 

 seeds when forcibly disturbed, but not otherwise to drop 

 them. The Poppies, Wild Hyacinth, Henbane, and various 

 caryophyllaceous plants, have capsules erect in fruit and 

 opening above, and the stems become stiff and elastic when 

 the seeds are ripe. In some plants such as Erodium, the 

 seed can actually crawl away from the parent. Certain 

 trees, such as the Ash, Maple, Hornbeam, and Pine possess 

 winged fruits which when detached by a breeze tend to be 

 carried short distances, clear of the shadow of the parent, 

 though the seed itself is of considerable weight. They com- 

 bine in this way the advantages of a large embryo, which 

 gives the young plant a copious store of nutriment to draw 

 from while it is competing with the short herbage, with a 

 seed sufficiently mobile to reach places where it can obtain 

 sunshine and new soil. 



The majority of our plants, as already remarked, have 

 other means of dispersal, which will enable the species 

 occasionally to overleap barriers — a faculty very different 

 and probably far more important than the slow spreading 

 over short stages that has just been spoken of. Here it 

 may be pointed out that this conquest of the land foot by 

 foot or yard by yard is insufficient to account for the 

 present distribution of our flora. It cannot surmount 

 barriers, and will not account for the mode of occurrence 

 of such a plant as Erica ciliaris^ which occupies in profusion 

 two compact areas, one in Cornwall and one in Dorset, 

 and has every appearance of spreading in each case from a 



