42 



which have been made regarding the longevity of seeds''^' 

 have proved that so far a hundred years may be taken as 

 the longest period for which seeds have been known to 

 retain their powxr of germination. The seeds which enjoy 

 such prolonged vitality belong to a restricted number of 

 Natural Orders of which the Pea Family is one, remark- 

 able like the others for the very resistant coat or testa with 

 which its seeds are covered. 



After the resting period, seeds when placed in favour- 

 able conditions commence to germinate. Moisture and a 

 warm temperature javoiir germination. Water is absorbed 

 by the seed coat as a whole, or may be taken in at certain 

 points. In some small smooth seeds the outer layers of the 

 seed coat are mucilaginous, and when whetted swtII up 

 considerably and become slimy. I'his is the case with 

 the seeds of the flax plant (linseed) and with those of the 

 cress. The probable reason for this special provision is to 

 cause the seeds to become fixed in the soil so that the 

 seed leaves can be more readily withdrawn from the seeds. 

 There are generally present on the inside of the seed coat 

 certain layers of cells which swell up rapidly when the 

 seeds absorb water, and probably aid in the splitting of 

 the seed coat, thus enabling the embryo to be gradually 

 withdrawn from the seed. Warmth, the other factor 

 essential to germination, is required for certain important 

 chemical changes which need to take place before germina- 

 tion can be effected. The food material stored in the seed 

 is largely of a solid nature and requires to undergo trans- 

 formation so that it can be dissolved in the cell-sap and 

 can be conducted to the growing root tip and to the 

 developing leaves. By certain fermentative changes starch 

 is converted into sugar, oil and organic nitrogenous com- 

 pounds are broken up and pass from cell to cell. In 

 some cases as in peas and beans the food material is stored 

 in the two fleshy seed-leaves or cotyledons, while in other 

 seeds like those of the melon, the onion, and in all our 

 cereals it is found in cells outside the young seedling and 

 requires to be absorbed by the latter before it can be made 

 use of at the growing points. The re-awakening of the 

 vital processes indicated by these internal changes is 

 marked by the commencement of respiration, that indis- 

 pensable accompaniment of all life, whether animal or 

 * Ewart, A. J. " On the Longevity of Seeds. Proceedings of 



the Royal Society of Victoria, igoS. 



