7IO CHEMICAL PROCESSES IN THE PLANT. 



to be formed at the expense of the starch which has been produced there ; this con- 

 clusion being derived especially from the observation of what takes place in Spirogyra 

 and Cereus^. 



The result of tracing by micro-chemical observation the products of assimi- 

 lation in the conducting tissues leads once more to the conclusion that the starch 

 which is formed in the cells containing chlorophyll is subject to a variety of 

 chemical metamorphoses before it reaches the growing tissues and the reservoirs of 

 reserve-material. Even during the period of vegetation the substances which are 

 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 inulin which is conducted through the stem to the underground 

 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 these 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 Cruci- 

 fers, 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 chlorophyll 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 

 Alg3e ; 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 (with the assistance of the constituents of the 

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



• ^ [Briosi states (Bot. Zeitg. 1873) that starch-grains are never found in the chlorophyll-granules 

 oi Musa and Strelitzia, but that drops of oil are present instead. His observations have been shown 

 to be erroneous by von Holle and Godlewski (Blora, 1877). Pringsheim (Ueb. Lichtwirkung und 

 Chlorophyllfunction, Jahrb. f. wiss. Bot. XII, 1880) enumerates a number of plants in which oil 

 is present, and not starch, in the chlorophyll-granules ; Vaucheria sessilis, Selaginella, Cycas, Stratiotes 

 aloides, Lilhun Martagon, Olea europcza. Begonia. He is of opinion that the first product of 

 assimilation is a waxy substance to which he gives the name of Hypochlorin.'] 



