METASTASIS. 181 



238.— The Storing of Reserve Material. In many plants 

 the surplus of assimilated matter is stored up in one or more 

 organs as reserve material ; thus in the potato the starch 

 formed in the leaves in sunlight is, in darkness, transformed 

 into glucose, or a substance very nearly like it, and in tliis 

 5oluble form it is diffused throughout the plant, and in the 

 underground stems (tubers) is again transformed into starch. 

 So in the case of many seeds a mass of reserve material is 

 stored up, generally in the form of starch {e.g., the cereal 

 grains), and sometimes in the form of oily matters {e.g., the 

 seeds of Cruciferse, Flax, Castor Bean, Cucurbitacese, etc.). 

 In the storing of starch a notable feature of the changes which 

 take place is the apparent addition and subtraction of one 

 or two molecules of water ; it is probable, however, that in 

 the transformation of starch to glucose oxygen combines 

 with some of the carbon, forming free carbon dioxide, as 

 follows : 



6 (0,, H,„ 0,„) + 24 = 5 (C,, H,, O.J + 12 CO,. 



The transformation of glucose to starch may be a simple 

 process of breaking up of a molecule of the former into starch 

 and two molecules of water, as follows : 



C.,H,,0„ = C„H,„0,. + 3H,0. 



In the storing of oily matters it is probable that these are 

 formed at the expense of the starch, and that they are the 

 results of subsequent deoxidation. 



237.— The Use of Beserve Material. In the use of re- 

 serve material, as in the germination of a starchy seed, the 

 starch appears to undergo a change exactly like that in its 

 disappearance from chlorophyll. Here it is certain that oxy- 

 gen is absorbed, and that carbon dioxide is evolved, while 

 the starch is transformed into glucose (see the reaction above) 

 Similar ■ transformations doubtless take place in the use of 

 the starch stored up in buds, twigs, stems, bulbs, etc. In 

 the germination of oily seeds, after the absorption of oxy- 

 gen, starch is (in many cases, at least) first produced, and 

 from this the soluble sugar is formed. In any case, after the 

 solution is attained the subsequent metastatic changes are 



