RESPIRATION. 491 



which flamed so recently tints of red gold between the dark mountain pines, are 

 now covered with dazzling white from the winter sky. 



3.— PROPELLING FORCES IN THE CONVERSION AND 

 DISTRIBUTION OF MATERIALS. 



Eespiration. — Development of Light and Heat. — Fermentation. 



RESPIRATION. 



One of the most remarkable things about metabolism in plants is that every 

 species is its own model and type, that the compounds which are manufactured 

 in various species always remain the same in successive generations, and that from 

 the same soil, the same water, and the same air, under equal illumination and under 

 the influence of the same temperature, the most difierent organic compounds are 

 prepared by various species situated in close proximity. Within an area of a 

 square metre spring up from the forest soil the poisonous Boletus sanguineus, the 

 savoury Mushroom, and the latex-swollen Russula; and if the seeds of Mustard, 

 Corn-cockle, and Poppy (Sinapis nigra, Agrostemma Githago, Papaver Rhoeas} 

 are strewn on a garden bed of uniform soil, so that the plants germinated from 

 these seeds grow simultaneously side by side, their seeds will indeed exhibit 

 materials of the most varied composition, but every mustard seed, every seed of 

 the corn-cockle, and every poppy seed will present exactly the same compounds 

 as were possessed by the seeds sown, compounds which the seeds of these species 

 have contained for thousands of years. This phenomenon can only be explained 

 by the association of like to like always and everywhere in the plant, and by the 

 supposition that every molecule of a certain material not only operates as a 

 centre of attraction on its surroundings, but that the attracted atoms are grouped 

 according to the special type, just as happens in the crystallization of mineral 

 substances. 



If the atoms in the colourless cells of a seed germinating in the darkness of 

 the soil are attracted in the manner indicated, arranged in a certain way, and 

 connected together to form a solid body, the chemical equilibrium in those cells 

 must be disturbed. If the materials thus attracted were previously dissolved in 

 the sap of these cells, the degree of concentration of their sap must have been 

 diminished in consequence of their withdrawal, and will be less than that of the 

 neighbouring cells. But this dissimilarity cannot be maintained, and therefore 

 a compensating movement occurs, which spreads to more and more distant cells; 

 or, in other words, the materials stream towards the places of consumption. "We 

 return to this process, already once described, in order to review the propelling 

 forces which are concerned in the metamorphoses and distribution of the materials. 



