Vivifying Power of Light and Heat. 149 



the ordinary fern of the north is the tree-fern, in place of 

 common grass the bamboo, in place of simple moss the 

 Neckera dendroides or some other tree-moss. Here, 

 indeed, where all plants have a tendency to become 

 ligneous as well as arborescent, one or other plant is 

 always in flower, and no plant is ever leafless. 



The lesson to be gathered from these facts is plainly 

 this that plants owe their very existence to the sun, 

 and that their vital vigour is directly proportionate to 

 the degree of insolation to which they are exposed. It 

 is indeed only another version of the annual history of 

 vegetation in the temperate regions of the globe, for here 

 the state of things inclines to that met with in high 

 northern latitudes as the earth turns away from the sun 

 in winter, and to that which is natural to equatorial 

 regions when the earth turns towards the sun again in 

 summer. Moreover, what happens every twenty-four 

 hours may be supposed to convey a hint to the same 

 effect, for the wakefulness of plants in the daytime and 

 their sleepiness at night, as seen in the opening and 

 shutting of flowers, in the rising and falling of leaves, 

 and in many other ways, are in fact only partial mani- 

 festations of the more marked summer and winter changes 

 in the life of plants, which are distinguished as aestivation 

 and hybernation. 



Nor is the case altogether different when the atten- 

 tion is directed from the world of plants to that of 

 animals. 



A few hardy animals, like the polar bear, and wolf, 

 and reindeer, can brave the terrors of the polar cold and 

 darkness, but the majority, like the marmot, must 

 migrate southwards as the winter approaches, or else, if 

 they do not die outright, sink into the death-like sleep 

 of hybernation until revivified by the returning spring. 



