8 THE BOOK OF NATURE STUDY 



When they are first seen above ground they are pressed together 

 looking like one leaf. Compare with these the seedlings of the 

 seeds that were sown three days later. They are not yet above 

 ground, therefore in order to see them the surface soil must be 

 gently scraped away. The hypocotyl will be seen in the form of 

 an arch, like the letter U turned upside down ; the cotyledons 

 may be still within the seed, or possibly they may have just 

 emerged. If they have come out. of the seed, note that they are 

 yellow, not green. It is by means of the arch that the hypocotyl is 

 able to drag the seed-leaves out of the seed. As soon as the arch of 

 the hypocotyl rises above the soil the two limbs of the arch begin 

 to separate, this allows the inner surface of the arch to grow more 

 quickly than the outer. The limb of the arch nearest the seed is 

 helping to keep the seed fixed in the soil, whilst the other is 

 tugging away vigorously at the seed-leaves, pulling them out of the 

 seed. As soon as the cotyledons have been dragged from beneath 

 the ground the hypocotyl 'straightens itself, the two seed-leaves 

 which had been pressed together separate, turn green owing to the 

 influence of light, and begin to make food for the young plant. 



SEEDLING OF PEA. The pea and bean seeds behave differently. 

 To begin with, they grow rather more slowly than the mustard or 

 radish. Nothing could be seen above the soil till sixteen days 



after the seeds were sown. 

 The broad bean was slower 

 than the pea, and the kidney 

 bean the slowest of the three ; 

 it was nearly three weeks 

 before there was any sign of 

 growth above the soil in the 

 case of the broad bean. The 

 cotyledons of these three seeds 

 remain in the ground, the 

 _ epicotyl, or plumule not the 



FIG. 3. Seedling of pea. , 



hypocotyl making its way 

 through the soil. Here, again, the arch form may be observed, by 

 clearing away the upper layer of soil and examining peas or beans 

 in different stages of development. 



