THE DISPERSION OF SEEDS AND SPOUES. 125 



acquaintance with the habits of man in a state of 

 savagery. The arts of civilisation have at least 

 exercised an important modifying influence on many 

 seeds and fruits. It hardly admits of doubt that 

 most of our cereals and a great many cultivated 

 flowers and fruits are now quite incapable of 

 perpetuating themselves apart from human inter- 

 ference. In a negative sense these varieties, if they 

 are not entitled to the rank of species, may be said 

 to have become dependent on man for dispersion. 

 It appears also probable that many weeds may have 

 been modified unintentionally in the same direction, 

 and have become through man's operations no longer 

 capable of maintaining their existence apart from 

 his activity. Were a country left to itself, it is 

 reasonable to suppose that with the disappearance 

 of the wheat, oats, and other cultivated grains, some 

 of the weeds which invariably accompany cultivation 

 would also disappear. The small seeds of the poppy, 

 mustard, spurrey, and other weeds of the cornfield, 

 are well adapted, at any rate, to take advantage of 

 man's agricultural operations, and thus make him 

 an unwilling agent in their dispersion. But doubtless 

 the greater number of the changes which man has 

 unintentionally effected on the distribution of plants 

 are due to the alterations in soil and climate brought 

 about by his operations. The construction of drains 

 and mines, quarrying, and other excavations fre- 

 quently turn up seeds that have long lain dormant, 

 and give rise to changes in the flora. The cutting 

 down of woods, the erection of buildings, the 

 concentration of population in great centres, and 

 the constant traffic between place and place must 

 have led to the extermination of many species and 

 the occupation of their places by others. One 

 example of the changes brought about by these 

 means — a case which came under the writer's 

 observation lately — may be mentioned. Numerous 

 plants of Lepidium Draba mysteriously appeared on 

 a new railway embankment in a locality where the 



