52 BREEDING 



almost the entire space within the seed-coat; and, 

 lodged between them — and, of course, attached to 

 them — are seen the little shoot and root, which 

 are all there is, as yet, of the embryo plant. 



These two cotyledons (which are the hemi- 

 spheres which constitute " split peas ") are supposed 

 by some botanists to represent leaves which have 

 become greatly modified in accordance with their 

 having taken on a function not usually performed 

 by leaves, namely, that of acting as a storehouse 

 of food material for the young plant. Unlike 

 ordinary leaves, these cotyledons do not come 

 above the ground when the seed germinates. In 

 the case of many plants, however (as, for instance, 

 the sunflower), in which the cotyledons are less 

 specialised as storehouses of food material, they 

 do come above the ground ; and, although in the 

 latter case they behave physiologically like ordinary 

 leaves, they nearly always differ in shape from 

 the other leaves of the plant. 



The whole of this store of food material is laid 

 down in the first two leaves (or cotyledons) of the 

 embryo plant before the embryo pea-plant has 

 become detached from its parent. In other words, 

 the food material in the first two leaves of our 

 plant of the second generation is being laid down 

 whilst that plant is undergoing its early develop- 

 ment within the seed-coat, which, as we have said, 

 is a part of our plant of the first generation, 

 just as the embryo of a mammal is nourished in 

 the womb. In fact, the womb with its contained 



