ONION 19 



the seed and cutting towards the narrow end. Note the white embryo with 

 its well-marked radicle, hypocotyl and two flat cotyledons lying within the 

 semi-transparent endosperm. 



12. Some of the most commonly occurring endospermous 

 seeds will be found to have embryos within them which are not 

 dicotyledonous, and whose structure is in many respects very 

 different from those we have hitherto mentioned. A good 

 example is met with in the onion. 



Onion. — The seed is black, somewhat oval in outline, with 

 one side convex, the other almost flat. Each contains within it 

 endosperm and an embryo which lies curled up inside in the 

 form seen in i, Fig. 6. When germination commences, the 

 curved part (c) imbedded in the middle of the endosperm grows 

 and forces the end (a) of the embryo out of the seed. From 

 this exposed end, which is the radicle, a straight, slender, primary 

 root develops, the extent of which is seen at 3 and 5, Fig. 6. 



The part of the young seedling which extends from the root 

 into the interior of the seed, grows very rapidly at first, at 

 the same time assuming a sharply bent outhne (2, Fig. 6). It 

 comes above ground in the form of a close loop (<r), but on further 

 growth the end within the seed is pulled out of the soil, and 

 grows up in the air. The tip within the seed changes and 

 absorbs the endosperm, and usually remains there until all the 

 nutrient material has been transferred from it to the various 

 centres of growth in the young plant. After the food-reserve 

 is exhausted the tip withers and becomes free from the seed-coat. 

 In loose soils the latter is pulled above ground before the endo- 

 sperm is exhausted, and remains on the end of the tip for some 

 time. In other cases where the soil is damper and of a stiffer 

 nature the seed-coat remains below ground altogether. 



The curved part of the embryo which comes above ground 

 is a leaf. It is the cotyledon of the embryo, and is in reality a 

 thin hollow leaf like those of the full grown onion plant : within 

 it is the plumule, which consists of a series of hollow conical 



