196 FOOTNOTES FROM 



t 



essential to the wellbeing of the fungus. All other plants 

 are absolutely dependent upon light for their very 

 existence. Roses, tulips, sun-flowers, wait upon the 

 beams of the sun, and live only in his smiles. They 

 may be supplied with the requisite conditions of heat, 

 air, and moisture, but without light they will wither 

 and die ; or, if they do seem to grow, it is only a false, 

 unnatural, and sickly growth, losing their substance 

 instead of increasing it, and weighing less when dried 

 than the dry seed from which this amorphous growth 

 proceeded. Light is not required for the germination 

 of seeds ; but if the plant be suffered to grow up in 

 darkness, it merely uses up the store of food contained in 

 the seed, and when that is exhausted its further growth 

 is stopped. It can obtain no new food from without ; 

 for it is light alone that can occasion the decomposition 

 of the carbonic acid contained in the vessels of all the 

 parts exposed to its influence, and without this light 

 the plant could not assimilate the carbon to its own use. 

 It is a remarkable fact that the heat of the sun alone 

 will not enable the plant to perform this operation. It 

 must be exposed directly to the light of the sun ; and 

 every cloud in the sky, and every shadow from rock or 

 tree that obscures or hides this direct sunlight, retards 

 the vital activity of every plant on which such shadow 

 falls. The particular ray in the sunlight which produces 

 this intense effect upon the organization of plants, has 

 been separated by physiologists. By causing plants to 

 effect the decomposition of carbonic acid in the prismatic 

 spectrum, Professor Draper, to whom we are indebted for 

 this interesting discovery, ascertained that the yellow 



