244 T^HE PHYSIOLOGY OF PLANTS 



§ 47. How should the ripe seed be treated ? 



The product of fertilisation, tlie seed, contains, as chief 

 constituent, the young plant or embryo. The latter is gene- 

 rally so far developed, that it shows the embryonic root or 

 radicle and the young shoot or plumule. Nature has also 

 provided for the early nutrition of the plant before the root 

 begins to function. The seed is for this purpose provided 

 with a mass of food material, which only requires to become 

 dissolved in order that it may be at once made use of by 

 the embryo. This food material, which is stored up chiefly 

 as starch or oil, is either contained in the seed-leaves or 

 cotyledons, if the embryo alone fills the seed, or in a special 

 parenchymatous tissue, the endosperm or albumen, in which 

 case tlie embryo is generally small as compared with the size 

 of the seed. In this latter case special arrangements are 

 made, by which the absorption of the dissolved food material 

 by the embryo is as easily effected as if the food material 

 were stored up in the cotyledons. 



Besides their economic importance as food materials for 

 man, the seeds must be considered also with regard to the 

 future production of new plants. The chief value of seeds 

 indeed is the reproduction of the species to which they belong. 

 This reproduction is sometimes effected immediately after the 

 ripening of the seeds, but generally they pass through a 

 resting period of some length. We must, therefore, first con- 

 sider the resting and then the germinating* seed. 



The fully mature and garnered seed is by no means lifeless. 

 A number of insufficiently known changes take place within 

 it, which cause it to give off water and carbonic acid, and also 

 to change its colour. We must also assume that during the 

 resting period ferments are formed which cause the rapid 

 solution of the food material during germination. This may 

 be gathered from the fact that seeds of the same kind and of 

 the same crop will under similar conditions require a longer 

 time for germination, the further off they are from the normal 

 time of germination. 



The chief condition for securing germination is the requisite 

 supply of water, besides an increase in temperature and in the 



