ASSIMILATION AND METASTASIS. 707 



substances of this kind to particular species of plants shows that they are not 

 of the same significance as the former. They may be of great importance for 

 the growth of the species; but more accurate knowledge is still wanted in all 

 cases. 



Since seeds, tubers, and other parts of plants that are filled with reserve-material 

 can be made to unfold buds, to put out roots, and even to form flowers and the 

 rudiments of fruits by supplying them with pure water and oxygenated air when the 

 conditions for assimilation (chlorophyll and sunlight) are absent, it follows that the 

 substances stored up in these reservoirs furnish the material for the growth of the 

 new leaves, roots, and flowers. The reservoirs are therefore emptied in proportion 

 as the growth of the new organs progresses ; and when finally they become com- 

 pletely empty, all further growth ceases, if sunlight and chlorophyll do not cooperate 

 to produce new formative material by assimilation. It is moreover easy to follow the 

 reserve-materials by means of micro-chemical reactions in their course from the 

 reservoirs through the conducting tissues to the growing organs, and to recognise 

 their relation to the growth of particular tissues. A close study leads first of all to 

 the conclusion that the albuminoids contained in the reservoirs of reserve-material 

 reappear as such in the protoplasm of the newly-formed organs, having, independ- 

 ently of temporary qualitative changes, only altered their position. On the other 

 hand it shows that the oily matter and the carbo-hydrates which had accumulated in 

 the reservoirs finally entirely disappear as such or leave only a small residue (oil) ; 

 while in their place a mass of new cell-walls is formed which were not in existence 

 before; and the material for the construction of these can only have been derived, 

 under the given conditions, from the carbo-hydrates, or, when these are absent, from 

 the oily matter which has now disappeared. If we thus come to the conclusion that 

 starch, sugar, inulin, and oil are the substances from which are formed the cell-walls 

 of plants, at all events in so far as they are nourished from a reservoir of reserve- 

 material, it by no means follows from this that the whole of the store is used up 

 entirely in the production of cellulose ; on the contrary a variety of other substances 

 are formed during growth, such as vegetable acids, tannin, colouring-matters, &c., 

 which are probably also derived from the same non-nitrogenous reserve-materials. 

 A part of the non-nitrogenous substance is also entirely destroyed and converted into 

 carbon dioxide and water, a process which may cause a loss of 40 or even 50 per 

 cent, of the weight of the organic substance of those seeds which germinate in the 

 dark. 



If the reserve-materials stored up in different seeds, tubers, bulbs, &c. are 

 compared, it is seen that starch, the various kinds of sugar, inulin, and oil, are 

 of the same physiological value with regard to their most important purpose, viz. 

 the formation of new organs ; inasmuch as these substances can replace one another. 

 Thus the cell-walls of the embryo of Allium Cepa are formed at the expense of 

 the oily matter of the endosperm ; but the cell-walls of the leaves and roots which 

 grow from the bulbs evidently obtain their formative material from the glucose-like 

 substance which fills the bulb-scales in a state of solution. In the Beet cane- 

 sugar is stored up for the same purpose, inulin in the tubers of the Dahlia, and 

 starch in the tubers of the Potato, the bulbs of the Tulip, &c. ; and these are 

 subsequently consumed. But in most seeds all these carbo-hydrates are replaced 



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