>jO MOLECULAR FORCES IN THE PLANT. 



essential properlies of protoplasm ; but various other substances penetrate between 

 its molecules and are afterwards again separated. This is especially observable in 

 the formation of zygospores and swarmspores. 



The nutriment and growth of organised structures takes place, as has already 

 been shown in Book I, by intussusception ; the nutrient solution penetrates between 

 the molecules already in existence, and either occasions by apposition an enlarge- 

 ment of the- individual molecules ; or new molecules of small size are produced in 

 the spaces filled with water, which then increase by the apposition of new matter, or 

 the increase takes place in both ways at different points. The increase in mass of 

 the cell-wall, starch-grain, &c., is therefore brought about by the molecules being 

 forced apart from within. Connected with the growth of the molecules already in 

 existence and with the formation of new ones, is a continual disturbance of the 

 osmotic equilibrium between the surrounding fluid (the cell-sap in the widest sense 

 of the term, see p. 62), and that within the body, which has the effect of constantly 

 drawing fresh particles from the surrounding fluid to the interior of the body which 

 is undergoing augmentation. 



Chemical processes in the interior of the growing body are also always con- 

 nected wnth these processes of growth. The nutrient fluid which penetrates from 

 without contains in fact the material for the formation of molecules of a definite 

 chemical nature ; but this material is chemically different from the molecules which 

 it produces. Thus starch-grains are nourished by a fluid which clearly does not 

 contain any starch in solution ; and again the cell-wall grows by the absorption of 

 substances out of the protoplasm which are not dissolved cellulose. The colouring 

 matter of the chlorophvH arises in the interior of the chlorophyll-grain ; and the 

 substances by which the protoplasm is nourished by intussusception are clearly 

 only produced in the interior of the protoplasm, as is shown in particular by naked 

 Plasmodia and by unicellular Algae and Fungi. Growth by intussusception is 

 therefore connected not only with a continual disturbance of the molecular equi- 

 librium, but also with chemical processes in the interior of the growing structure. 

 Chemical combinations of the most various kinds take place between the molecules 

 of an organised body, so tlvat they act upon and decompose one another. It is 

 certain that all growth continues only so long as the growing parts of the cell are 

 exposed to atmospheric air ; the oxygen of the air has an oxidising effect on the 

 chemical comipounds contained in the organised structure ; with every act of growth 

 carbon dioxide is produced and evolved. The equiHbrium of the chemical forces is 

 also continually disturbed by the necessary production of heat ; and this may also 

 be accompanied by electrical actions. The movements of the atoms and molecules 

 w'ithin a growing organised body represent a definite amount of work, and the equi- 

 valent forces are set free by chemical changes. The essence of organisation and 

 of life lies in this : — that organised structures are capable of a constant internal 

 change ; and that, as long as they are in contact with water and with oxygenated 

 air, only a portion of their forces remains in equilibrium even in their interior, and 

 determines the form or framework of the whole ; while new forces are constantly 

 being set free by chemical changes between and in the molecules, which forces in 

 their turn occasion further changes. This depends essentially on the peculiarity of 

 molecular structure, which permits dissolved and gaseous (absorbed) substances to 



