Vegetable Physiologij. 405 



the fact that most frequently the starch-granule does not contem- 

 poraneously diminish in size, hut in fact often grows larger. 

 Even in such peculiar cases as that of the potato-tuber " greened " 

 by exposure to light, the circumstance that the chlorophyll of 

 the outer layers of cells, which contain little or no starch, is 

 formed in the protoplasmic substance, warrants the supposition 

 that in the more deeply-seated starch-cells those starch-granules 

 which become coated with a layer of chlorophyll received this as 

 a deposit from the protoplasmic substance which we know to 

 exist diffused through the cell, and that the starch-granules are 

 probably dissolved and diffused in the cell-sap before being 

 utilised for new developments. 



The evidence, then, furnished by the history of development 

 of chlorophyll- and starch- granules, leads us to conclude that the 

 relation of starch to chlorophyll is chiefly, if not entirely, de- 

 pendent on the fundamental identity of the albuminous substance, 

 forming the material basis of the chlorophyll-granules, with the 

 protoplasm or nitrogenous formative matter of the cell. 



The matters belonging to the cell-contents, which have up to 

 this point been examined, are at once substances very generally 

 ■when not universally diffused in the vegetable kingdom (the 

 Fungi affording the exception as regards chlorophyll and starch), 

 and at the same time accessible to microscopic investigation. 

 Various other products remain to be enumerated, to which those 

 characteristics only apply partially, or are even inapplicable. 



Fatty matters or fixed oils may be regarded as very generally 

 present in plants, and they occur for the most part in ccmditions 

 analogous to those in which starch is found ; indeed, fixed oil 

 is not unfrequently found replacing previously existing starch- 

 granules in the very same cells, possibly through a transforma- 

 tion. Oils are ojften to be detected, by the microscope, by their 

 standing suspended in drops of variable size in the cell-sap. If 

 abundant, the drops are often large, and their nature may be 

 <letermined not merely by their optical characters, but by their 

 •confluence under pressure and their solubility in ether (fig. 4, e). 

 In living cells they are never in immediate contact with the cell- 

 membrane, but lie inside the albuminous lining of the cell, and 

 adherent to the masses of protoplasm. In many cases where the 

 oil is in small quantity it is so intimately combined with albu- 

 minous substance that it cannot be detected by simple inspection 

 under the microscope ; but heating the cells, so as to solidify the 

 albuminous matters, often causes the separation of the oil in 

 drops. Drying up oil-bearing cells will likewise cause conflu- 

 ence of the drops, and, when the albuminous lining of the cell 

 is destroyed or injured, the oil readily soaks out through the cell- 



VOL. XVIII. 2 K 



