CHANGES IN THE SEED DURING- GERMINATION. 297 



620. Woody species thus seem to preserve the power of germinat- 

 ing longer than others, while biennials are at the opposite end of the 

 scale ; perennials would appear to lose their vitality sooner than an- 

 nuals. Large seeds were found to retain the germinating power longer 

 than small ones, and the presence or absence of separate albumen or 

 perisperm did not seem to make any difference. Composite and Um- 

 belliferae lost their germinating power very early. From these experi- 

 ments, Decandolle concludes that the duration of vitality is frequently 

 in an inverse proportion to the rapidity of the germination. This 

 subject is now being investigated by a committee of the British Asso- 

 ciation, under the direction of Professor Daubeny. 



621. <) IM-III ifl changes daring Germination. During the process 

 of germination, certain changes take place in the contents of the seed, by 

 which they are rendered fit for the nourishment of the embryo. In 

 exalbuminous or aperispermic seeds, where the embryo alone occupies 

 the interior, these changes are effected principally in the matters stored 

 up in the cotyledons. In albuminous or perispermic seeds, on the 

 other hand, the changes occur in the substance of the perisperm. One 

 of the most remarkable of these changes is the conversion of starch into 

 dextrine and grape sugar by a process of oxidation, the object being 

 the conversion of an insoluble into a soluble substance. A nitrogenous 

 compound, called Diastase (^[ 310), is developed during germination, 

 and is said to act on the starch. This diastase may be probably a por- 

 tion of gluten passing into a state of decomposition, and acting as a 

 ferment. The change of starch into dextrine and sugar is referred 

 by chemists to catalytic action, or the action of contact, and to the 

 influence exercised by diastase and other matters in making a new 

 arrangement of the molecules. While this conversion of starch into 

 sugar proceeds, oxygen is absorbed, carbonic acid is given off, and 

 heat is produced. These phenomena are well seen in the malting of 

 barley. The changes produced in the air by germinating seeds have 

 been investigated by Saussure, who showed that in all cases carbonic 

 acid was evolved at the expense of the carbon of the seed. 



622. When all the requisites for germination are supplied, the seed, 

 by the absorption of moisture, becomes softened and swollen. When 

 albumen or the perisperm is present, it undergoes certain chemical 

 changes by the action of the air and water, so as to be rendered fit for 

 the nutrition of the embryo. These changes consist partly in the con- 

 version of starch into sugar, and are accompanied with the evolution 

 of carbonic acid, and the production of heat. As the fluid matters are 

 absorbed by the cells of the embryo, the latter continues to increase 

 until it fills the cavity of the seed, and ultimately bursts through the 

 softened integuments. In cases where there is no perisperm, the exal- 

 buminous embryo occupies the entire seed, and the process of germi- 

 nation goes on with greater rapidity. The embryo speedily swells, 



