GERMINATION OF A SEED 23 



Having soaked a bean for several hours till it has 

 become swollen, remove it from the water and keep it 

 on damp boiled sawdust or in some moist situation in 

 an ordinary room for some days. After a short time the 

 young radicle will be found to protrude from the micro- 

 pyle and to grow downwards. The cotyledons swell 

 and the testa cracks and begins to slip off. The plumule, 

 which was seen to be curved inwards, elongates ; the 

 curvature becomes more marked and forms a loop 

 which emerges from between the cotyledons ; it finally 

 straightens itself and thenceforward grows vertically 

 upwards. This loop is formed from the part just 

 above the cotyledons which is known as the epicotyl. 

 The cotyledons remain much as they were, but as the 

 seedling grows their contents are gradually absorbed 

 by the axis and they shrivel away. In their normal 

 development when the seed is below the surface of the 

 earth the cotyledons remain buried. The advantage of 

 the looped epicotyl is seen as it presses upward through 

 the layer of soil above the seed, for the delicate leaves 

 of the plumule are saved from the injury which they 

 would suffer if they had to force their way through the 

 earth. The epicotyl in fact opens a passage for them. 



Some seeds whose structure is almost identical with 

 that of the bean behave a little differently in germina- 

 tion. The part of the axis which elongates and brings 

 the plumule through the soil is a region a little below the 

 cotyledons, and it is consequently called the hypocotyl. 

 The lengthening of this part causes the cotyledons also 

 to be carried up into the air, and after a short time they 

 turn green, and take on the work of the foliage leaves 

 which are developed as the plumule grows. 



When the castor oil seed germinates the early stages 

 are much the same as in those of the bean. The seed 

 swells and the radicle grows through the micropyle, and 

 very_soon the young root branches freely. The endo- 



