194 THE FOOD AND NUTRITION OF PLANTS. 



temporarily insoluble form accumulated as the ready prepared ma- 

 terials of future growth (82). Notwithstanding the diiference in 

 their properties and chemical reactions, these and other general 

 ternary products (79) are strictly isomeric ; that is, they consist of 

 the same elements, combined in the same proportions ; and physi- 

 ologically they are merely different states of one and the same thing. 

 Dextrine is the most soluble state, and is probably that originally 

 formed in assimilation in the foliage : starch, amyloid (83), &c. are 

 temporarily solidified states ; and cellulose is the ultimate and usu- 

 ally permanent insoluble condition. Accordingly, whenever the ma- 

 terials of growth are supplied from accumulations of nourishment, 

 as especially from the seed in germination, (123- 125), from fleshy, 

 roots (145), rootstocks, tubers, &c. (188-194), the starch or itsp 

 equivalent is dissolved in the sap, being spontaneously reconverted! i 

 into dextrine and sugar, and attracted in a liquid state into thei ' 

 growing parts, where, transformed into cellulose, it becomes a por- 

 tion of the permanent vegetable fabric. 



350. If, however, we suppose sugar to be a direct product of the 

 assimilation of carbonic acid and water, the amount of oxygen gas 

 exhaled will be just the same as before. For this has the same 

 elementary composition as dextrine, starch, and cellulose, with the 

 addition of one or two equivalents of water according to the kind.* 

 And when formed as a transformation of dextrine, then the latter 

 has only to appropriate some water. In the origination of all these 

 products, therefore, the same quantity of carbonic acid is consumed, 

 and all its oxygen restored to the air.f It is more and more evident. 



* The formula for cane-sugar is C12, Hii, On ; for grape-sugar, C12, Hu, O12. 



t Since all these neutral ternary substances are identical, or nearly so, in ele- 

 mentary composition, and since, with the same amount of carbon, derived from 

 the decomposition of carbonic acid, the plant can form them all, it will no longer 

 appear surprising that they should be so readily convertible into each other in 

 the living plant, and even in the hands of the chemist. But the chemistry of 

 organic nature exceeds the resources of science, and constantly produces trans- 

 formations which the chemist in his laboratory is unable to effect. The latter 

 can change starch into dextrine, and dextrine into sugar ; but he cannot reverse 

 the process, and convert sugar into dextrine, or dextrine into starch. In the 

 plant, however, all these various transformations are continually taking place. 

 Thus, the starch deposited in the seed of the Sugar-cane, Indian Com, &e. is 

 changed into sugar in germination ; and the sugar which fills the tissue of the 

 stem at the time of flowering is rapidly earned into the flowers, where a portion 

 is transformed into starch and again deposited in the newly-formed seeds. And 



