ASSIMILATION AND METASTASIS. 
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 Jahrbücher für wissenschaftliche Botanik, 
vol. III. p. 183 et seq. ; Flora, 1862, pp. 129 and 289, and 1863, pp. 33 and 193 ; and have 
