THE PURPLE SAXIFRAGE 91 



and shoots, enlargement of roots, and the like. The fact 

 that they are capable of rapid adaptation has made it 

 possible for certain plants to maintain themselves on high, 

 bleak, wind-swept mountains and on arctic shores, as well 

 as in the sheltered lowlands of temperate regions. The 

 absence of visible adaptation to extremely hard climatic 

 conditions is, however, equally remarkable. Take the list 

 just given (p. 90) and see how few of the plants named 

 could have been set down as arctic-alpine by mere con- 

 sideration of their structure. 



Insufficient attention has, I think, been paid to the acts 

 of man in draining and reclaiming wastes. There can be 

 no doubt that many European plants, now restricted to 

 high or northern tracts, could perfectly well endure a mild 

 climate, if they were left undisturbed by draining, mowing, 

 grazing, and the competition of introduced species. A 

 cause so apparently slight as the application year by year 

 of a particular chemical manure has been found to affect 

 visibly the proportions of particular species in the herbage. 

 Thus it has been found at Rothamsted that the product 

 of a tract of unmanured permanent grass-land included 

 nearly 50 species, viz. about 17 grasses, 4 leguminous 

 plants, and 27 species of other families. By vigorous 

 manuring for many years continuously, the number of 

 species was reduced to 15, the leguminous herbage becom- 

 ing excluded altogether, and the miscellaneous herbage 

 nearly so. Purely mineral manures reduce the percentage 

 by weight of grasses, and increase the percentage by weight 

 of leguminous plants in the hay, while they reduce both 

 the number of the species and the proportion by weight 

 in the hay of the miscellaneous herbage. In the same 

 way where a farm immediately adjoins a moor there is 

 often a striking contrast between the vegetation which 

 has been grazed and manured and that which has been 

 left in a state of nature. A wall may thus come to separate 

 two plots which are occupied by two quite different assem- 

 blages of plants. 



