34 OUR FAEM CROPS. 



when sown, may have been too dry to allow of the absorp- 

 tion by the seed of sufficient moisture for its purpose ; or 

 it may have been too wet, and thus kept the temperature 

 too low for the germinative process to be set up ; or the 

 seed may have been left too near the surface, and exposed 

 to the action of too much light ; or it may have been 

 deposited too deep to admit of that access to the air which 

 is absolutely necessary to carry out those changes which 

 the vital principle existing in the germ of the seed sets in 

 motion before the plant can be produced. 



Let us suppose, however, that we have secured all these 

 desirable conditions that the seed has been deposited in 

 the soil by one of the methods described, and that the 

 germinative process has proceeded satisfactorily as vege- 

 tation advances we see the "plumula" gradually increas- 

 ing in length, until it shows itself above the surface, in the 

 shape of a slight cylindrical filament, which, on exposure 

 to the action of light, speedily changes from a pale yellowish 

 colour to a darker green, while at the same time a number 

 of very fine fibres or rootlets are being sent out from the 

 seed, downwards in different directions, through the soil, 

 as far as they can penetrate. If we were now to take up 

 the young plant and examine the state of the parent seed 

 which we had sown, we should find it little more than a 

 shrivelled husk all its interior having disappeared under 

 the influence of those changes which were necessary for 

 the support of the young plant ; while, if we were to take 

 the young plant itself, and submit it to a rigid analysis, 

 we should find its ultimate elements to consist merely of 

 those substances which before existed in the seed, but 

 combined together under different laws, in different propor- 

 tions, and with the addition of a large quantity of water"; 



The food of all plants consists of the two classes of 

 bodies, organic and inorganic; the portion of the plant 

 above ground has the duty of supplying the former, while 



