ASSIMILATION AND METASTASIS. 6^Q 



conducted to the young parenchyma of growing parts as soon as this has been 

 differentiated from the primary tissue, give rise to the formation of fine-grained 

 starch which accumulates there temporarily, and disappears with the final and rapid 

 increase in size of the cells. Starch and other substances are then produced afresh 

 by assimilation in the fully developed leaves ; and starch and the products of its 

 transformation again appear in the conducting tissues, not to be consumed there, 

 but only to be conducted to the still younger parts. The metamorphoses of the 

 formative materials which are conveyed from the assimilating organs to the re- 

 servoirs of reserve-material, generally show a reversed order of succession to that 

 which takes place during germination ; the starch produced in the leaves is trans- 

 formed in the leaf-stalks of growing beet into glucose, from which crystallisable 

 cane-sugar is formed in the swollen tuberous roots ; in the artichoke the starch is 

 converted into inuline which is conducted through the stem to the undergrountl 

 tubers ; in the potato, the mature leaves of which form starch, a substance similar 

 to glucose is chiefly found in the conducting tissues, which is conveyed to the 

 growing tubers, and there evidently forms the material from which the large 

 masses of starch are formed. In ripening fruits and seeds a large quantity of 

 glucose is generally found which disappears from the seeds when they become 

 ripe, starch being formed in the reservoirs of reserve-material; in Ricinus the oil 

 of the endosperm is evidently formed at the expense of the saccharine substance 

 which is conveyed to the seed; in the embryo of the same plant, as well as in 

 that of Crucifers, fine-grained starch is formed temporarily, which disappears when 

 the seeds are ripe, and is replaced by oily matter. 



Whether the albuminoids also are first formed in the assimilating cells which 

 contain chloroph}ll and whether they can be formed only in them, is still an unde- 

 cided point. It is certain that they are formed in the chlorophyll-containing cells of 

 Algae ; but it cannot be concluded from this that they can only be produced in the 

 corresponding cells of plants with differentiated tissues; at all events experiments 

 on the artificial production of the yeast-fungus show that it is able to form out 

 of sugar and an ammonium-salt or nitrate (with the assistance of the constituents 

 of the ash) not only cellulose but also albuminoids, as may be inferred from the 

 increase of the protoplasm in the rapidly multiplying cells. If the colourless cells 

 of yeast are able to do this, it may be inferred, until the contrary is proved, that 

 those cells of other plants which do not contain chlorophyll can also produce 

 albuminoids, if only a carbo-hydrate or oil (or both) is conveyed to them from 

 the leaves, and an ammonium-salt or nitrate from the roots. That the formation 

 of albuminoids probably takes place in this way within the conducting tissues of 

 internodes and petioles may be concluded from the deposition of calcium oxalate 

 in these tissues ; since in the formation of this salt sulphuric acid becomes separated 

 from the calcium, and its sulphur enters into the chemical formula of albuminoids \ 



When the cells of the leaves become emptied of their contents at the close 

 of the period of vegetation, and the deciduous parts fall, not only the starch which 

 was formed latest in the latter, but also the material of the grains of chloro- 

 phyll, is itself absorbed and conveyed through the leaf-stalks to the reservoirs of 



See 



Sachs, Handbuch der fIxpeiimental-Physiologie. p. 345. 



