58 THE GRASSES 



plant, growing in damp earth and exposed to the sunshine, 

 a current of fluid is setting from the root toward the sur- 

 face exposed to the air, where its watery part is for the 

 most part evaporated, while gaseous diffusion takes place 

 in the contrary direction from the surface exposed to the 

 air, through the air-passages and spiral vessels which ex- 

 tend from the stowates to the radicles; the balance of ex- 

 change being in favor of oxygen, in all the chlorophyll 

 bearing parts of the plant, which are reached by the sun- 

 light, and in favor of carbonic acid in its colorless and 

 hidden regions. At night, the evaporation diminishing with 

 the lowering of the temperature, the ascent of the liquid 

 becomes very slow, or stops, and the balance of the exchange 

 in the air-passages is entirely in favor of carbonic acid ; 

 even the chlorophyll bearing parts oxydizing, while no 

 carbonic acid is decomposed. 



In the foregoing has been given in plain and untechnical 

 language approved facts, which, under proper guidance, 

 every person of ordinary intelligence may be thought to 

 study amd to observe for himself. The general principle of 

 respiration, nutrition and reproduction of plants are, after 

 a century's scientific work, pretty well understood, although 

 a great deal of detail is yet to be investigated. 



Often, from impure motives, is science denounced as 

 "speculation." The growth of the pollen tube, and its 

 entrance into the ovule can be as clearly seen with the aid 

 of a medium power of a microscope as the siomata and 

 air-passages. That kind of speculation which is really to 

 be feared lies within the boundaries of ignorance. For in- 

 stance,, one can often hear assserted that the rust in the wheat 

 is caused by the iron present in the soil of the field. The 

 Agricultural Department in one of its recent volumes has 

 given to the farmers a very exact analysis of this distressing 

 phenomenon. In this, like in ever so many instances, it is 

 again proven that the greatest evils and plagues that affect 

 man and his operations, take their roots in the dispersion 



