248 THE PHYSIOLOGY OF PLANTS 



retain their vitality for a long time. Of a number of pine 

 seeds which were kept in a glass jar in a room for five years, 

 3 2 per cent, were germinated ; after seven years i 2 per cent, 

 had sufficient vitality to germinate. Of seeds stored in the 

 same way the following percentages of germination were 

 obtained : — Pted clover after twelve years, 10.5 per cent, ; peas 

 after ten years, 47.7 per cent.; linseed after six years, 49 

 per cent. ; after eleven years, 3 per cent. 



It is often stated that as the production of weakly offspring 

 increases with the age of the seeds, it is advisable to strengthen 

 their vitality by immersing them in dilute chloric, hydrochloric, 

 or some other acids. But the efficacy of this process has not 

 yet been established by experiment. It is possible, however, 

 that if the testa does not readily absorb water, the treatment 

 with acid might loosen the cells and effect a more rapid imbi- 

 bition. 



The second stage of germination, the solution of the food 

 material, requires, besides the water supply, above all things 

 an increase in the supply of oxygen. The seeds may even 

 dispense with some of the water — that is, their tissues need 

 not yet be saturated with water — for the commencement of 

 the vegetative changes to take place. If liquid water is not 

 available at the commencement, the seeds may condense and 

 absorb water from the atmosphere, and even absorb hydrogen, 

 nitrogen, and oxygen, like some porous substances. Grain 

 which has been swelled can take up more oxygen out of the 

 atmosphere than nitrogen, and the giving off of carbonic acid 

 takes place so actively, that more carbonic acid is given off 

 than can be accounted for by the amount of oxygen taken in. 

 This indicates that internal processes of oxidation (respira- 

 tion) are carried on in germinating seeds. This oxidation is 

 accompanied by an evolution of heat, and the latter again 

 increases the solution of the reserve substances. 



These now make their way to the seedling. If they are 

 contained in the cotyledons or seed-leaves, they will be 

 carried by the young vascular bundles to the root and stem 

 apices. If they are stored up outside the embryo in the 

 form of endosperm, the embryo will be provided with 

 special absorptive cells. In our grains (wheat, maize, &c.) 



