ASSIMILATION AND METASTASIS. 713 



tissues and the tubers ; and the accumulation of the whole of the reserve-material 

 in the tubers would be impossible. The glucose is used up in the tubers in the 

 formation of starch-grains ; and a fresh quantity therefore continually streams in 

 that direction; the whole mass of the material produced in the leaves is therefore 

 gradually transferred to these reservoirs of reserve-material. The starch is first 

 transformed into glucose, and then back into starch ; and it is in this chemical 

 process that the vehicle for the movement consists. Starch is even produced tem- 

 porarily in the conducting parenchyma, but of course cannot be transported as such 

 from cell to cell ; its movement being effected by the solution of grains in one cell, 

 the product of solution diffusing into the adjoining cell, and being there employed 

 in the formation of starch-grains which are then again dissolved, and so on. When 

 again cane-sugar is formed in the tuberous roots of the Beet, the movement towards 

 the root of the glucose which is produced from the starch assimilated in the chloro- 

 phyll is brought about in this way, — every particle of glucose undergoes chemical 

 transformation when it reaches the root, and the molecular equilibrium of the 

 solution of glucose is thus disturbed ; the root acting as a centre of attraction on 

 the glucose in the leaf-stalks. But the continual formation of the solution of 

 glucose in the leaves at the expense of the starch causes in them an increase 

 of concentration and a streaming of molecules towards the root, where the con- 

 centration of the solution of glucose is continually decreasing, while that of the 

 solution of cane-sugar increases. The same is evidently the interpretation of 

 the formation of inulin in the tuberous roots of the Dahlia and the tubers of the 

 Artichoke, and of that of oil in ripening seeds at the expense of the sugar which is 

 conveyed to them. 



I infer the co-operation in the movement towards the parts where the substances 

 are chemically altered, of the pressure exercised on the cell-sap by the tension of the 

 tissues, even where we have to do with closed cells, from the fact that considerable 

 quantities of the cell-sap appear on the surface of a transverse section of succulent 

 organs, both from the parenchyma and from the cambiform cells, and this is clearly 

 forced up by internal pressure. Since the tension and turgescence of the tissue are 

 always less in the buds and apices of the roots than in the older parts, there must 

 always be a tendency for the filtration of the sap towards the latter, which must act 

 in the same way as diffusion. 



That the contents of the perforated sieve-tubes and laticiferous vessels are 

 also subject to considerable pressure from the surrounding tissue is shown by 

 the extent to which these fluids flow out when the organ is cut through. The 

 fluid which is subject to pressure will have a tendency to escape from these tubes 

 to parts of the plant where the lateral pressure is less, which is the case in the 

 buds and apices of the roots. The flexions and distortions occasioned in the 

 organ by the wind will at the same time cause the fluid contents of the sieve- 

 tubes and laticiferous vessels to be pressed away from the older bent parts towards 

 the buds where the tension is less. 



The statements here compressed into a very brief space rest on a series of detailed 

 micro-chemical and experimental researches which I have described in the Botanische 

 Zeitung, 1859 and 1862-1865; Pringsheim's Jahrbiicher fiir wissenschaftliche Botanik, 

 vol. III. p. 183 et jeg.; Flora, 1862, pp. 129 and 289, and 1863, pp. 33 and 193; and have 



