THE SEED 83 



thing of the kind happens in coffee beans, so that only 

 the fresh beans contain cellulose capable of passing into 

 a soluble state. As to the last category of seeds, those 

 that sometimes require several years to germinate, such 

 as the seeds of stone fruits, the mere mechanical obstacles 

 they have to overcome may be regarded as one cause 

 of such a delay. Indeed germination can frequently be 

 accelerated by making incisions in the hard wall of the 

 seed. 



Let us now sum up all we have found out about the 

 phenomenon of germination, and let us try to define 

 the general characteristics of this unique period in the 

 life of the plant. 



The period of germination is unique because of the 

 fact that during its course the plant does not require 

 any external supply of food ; it subsists on the food 

 stored up in the endosperm or in the cotyledons. Three 

 factors are indispensable to arouse the seed to activity ; 

 these are water, the oxygen of the air, and heat. Water 

 acts in a twofold way : mechanically and chemically. 

 Mechanically, it causes the seed to swell, tears off its 

 membranes, and supplies the energy necessary for over- 

 coming the resistance of the surrounding particles of the 

 soil ; chemically, it first dissolves the various ferments, 

 and then with the help of these the insoluble substances 

 stored up in reserve. These solutions flow into the 

 embryo and are spent in its growth, in which they are 

 once more transformed into an insoluble or hardly 

 diffusible form. 



Respiration, apparently a function of every organism, 

 every living thing on the earth, with very few excep- 

 tions which will be mentioned later, manifests itself in 

 the germinating seed. At the same time it account 

 for the loss in dry weight and the rise in temperature, 

 noticed in germinating seeds. In this way the seedling, 

 in spite of its increase in bulk, not only shows no 



