LIMITS OF CULTIVATION. 379 



solar rays varies with the latitude. The effects of the 

 sun's rays in France and England in producing chemical 

 change are infinitely more decided than, with far greater 

 splendour of light, they are found to be in the lands 

 under or near the equator. Indeed, the remarks made 

 on the variations in the character of the sunbeam with 

 the changing seasons, may apply equally to the variations 

 in latitude. 



Fungals are among the lowest forms of vegetation, but 

 in these we have peculiarities which appear to link them 

 with the animal kingdom. Marcet found that mush- 

 rooms absorbed oxygen, and disengaged carbonic acid. 

 In all probability this is only a chemical phenomenon 

 of a precisely similar character to that which we know 

 takes place with decaying wood. In the conversion of 

 wood into humus, oxygen is absorbed, and combining with 

 the carbon, it is evolved as carbonic acid. Of course we 

 have the peculiar condition of vitality to modify the 

 effect, and we have, too, in this class of plants, the ex- 

 istence of a larger quantity of nitrogen than is found in 

 any other vegetating substance. 



These few sketches of remarkable phenomena con- 

 nected with vegetation are intended to show merely the 

 operations of the physical powers of the universe, so far 

 as we know them, upon these particular forms of 

 organization. During the process of germination, 

 electricity is, according to Pouillet, evolved ; and again, 

 in ripening fruits, there appears to be some evidence of 

 electrical currents. Vegetables are, however, in the 

 growing state, such good conductors of electricity, that 

 it is not, according to the laws of this force, possible 

 that they should accumulate it ; so that the luminous 

 phenomena stated to have been observed cannot be due 

 to this agency. We know, however, that under every 

 condition of change, whether induced by chemical or 

 calorific action, electricity is set in motion ; and we 

 have reasons for believing that the excitation of light 

 will also give rise to electrical circulation. 



