Ejfects of Snows and of Frosts. 23 



the sun's heat to pass through it with facility. The earth is thus 

 covered and protected from the intense cold of winter, the snow al- 

 lowing it to be warmed b)' the sun's heat, while at the same time it 

 does not allow the warmth of the earth to escape. The melting of 

 snows takes place largely from the under side, as we see evidence in 

 the vacant spaces around every object in the snow as the spring ap- 

 proaches. 



94. In forest shade the snow melts but slowly, and the water is 

 thus allowed to sink into the earth, or run off gradually, instead of 

 suddenly, as in the rains in an open country. By this delay in 

 melting, the vegetation is kept back until warm weather is con- 

 firmed and injuries from spring frosts are less liable to happen. 



95. In woodlands the snow does not drift, and this effect extends 

 somewhat into the adjacent fields, which are thus kept from ex- 

 posure to injurious frosts in winter. 



96. In liquid form the water is taken up by the roots, and with 

 it carbonic acid gas and various mineral substances in solution, the 

 latter supplying the inorganic portions remaining as ashes when the 

 plants are burned. In its chemical composition water consists of 

 two atoms of hydrogen united to one of ox3'-gen (Hj 0), and it is 

 produced when these elements are united by being burned together. 

 The agency of water will be further noticed in connection with the 

 functions of the leaves. 



Of tlie Effects of Frost. 



97. Many species of trees will not endure a freezing temperature ; 

 others are injured but not killed by it, and others appear fitted to 

 endure the greatest rigors of winter without injury, yet in excep- 

 tional cases even these may suffer from intense and prolonged cold. 

 The winters of 1683-4 and 1708-9 were memorable from the in- 

 juries they did in Europe to the forest trees, and in December, 

 1 879, a severe frost in France did immense damage to young tim- 

 ber. It was found on this last occasion that the injury was greater 

 where the sun struck the trees not protected by snow ; the effect 

 was greater in valleys than on high grounds, and varied much with 

 the soil, the exposure, and the humidity of the air. 



98. In these exceptional and fortunately rare cases, the condition 

 of the wood as to maturity had doubtless much influence, as the 

 winter appears to have found them unprepared for its rigors. It 

 was afterwards found, that many trees, supposed to be dead, still put 



