228 ROUND THE YEAR 



than those of its evergreen rivals, which are necessarily 

 minute, and this may possibly be a consideration of 

 weight. 



The leafy shoots of Ling and Bilberry, which seem 

 to spring out of crannies between rocks, are sometimes 

 borne upon long woody stems, which have made their 

 way up from a considerable distance. In rocky places 

 what look like tufts of low shrubs are sometimes the 

 tops of small trees. I have traced some of the ancient, 

 woody stems for many feet among the loose stones. 



It is, I think, worth while to attend to any peculiar 

 features of particular plants and animals, and to 

 interpret them as well as we can. But our interpre- 

 tations are never complete. We see some way into 

 the problem, and then are baffled by our ignorance 

 and by the complexity of the case. We can rarely 

 apply the experimentmn crucis, or find decisive in- 

 stances. There is always, or nearly always, as Goebel 

 says, some unknown quantity which decides why of 

 two plants similarly situated, one will show conspicuous 

 adaptations to its surroundings, while the other will 

 not. For this reason the methods of biological inquiry 

 are apt to be loose in comparison with the methods of 

 the physical sciences. In order to prove that the 

 height of the mercury in the barometer depends upon 

 the pressure of the air, we try to show that among 

 varying conditions of moisture, temperature, light and 

 so forth, the height of the mercury goes up or down 

 as one of these conditions, viz., the atmospheric 

 pressure, increases or diminishes. If it appeared that 

 the mercury was largely influenced by heat, or that 

 while some mercurial barometers rose and fell accord- 





