SEEDS 



323 



thinning or puncturing or breaking the hard seed coat, with- 

 out injuring the young plant (embryo), usually secures 

 prompt germination. The whole subject of delayed germi- 

 nation is under investigation, and it is evident that it is a 

 practical question of great importance. Experiments with 

 different seeds should be performed to discover the ordinary 

 variations in the ger- 

 minating period. 



The germination of 

 beans, which is rapid, 

 may be used as a pre- 

 liminary experiment. 

 Figs. 5-9 show some 

 of the stages. In Fig. 

 5, the tip of the hy- 

 pocotyl has broken 

 through the testa ; in 

 other words, the bean 

 has " sprouted." In 

 Fig. 6, the hypocotyl 

 is curving towards the 

 earth ; in Fig. 7, it 

 has elongated consid- 

 erably; in Fig. 8, it 

 has penetrated the 

 earth and put out 

 rootlets, developing a sharp arch. In Fig. 9, the root sys- 

 tem has gripped the soil, the cotyledons have been pulled 

 out of the testa, the arch has straightened, the young stem 

 bud (plumule) is seen between the cotyledons, and the seed- 

 ling has established itself for independent work. 



28. Depth of planting. There is no definite depth at 

 which seeds should be planted, for it varies with the condi- 

 tions. The thing to remember is that seeds should have 

 continuous moisture in a well-tilled soil. When seeds are 



FIGS. 5-8. A germinating bean : explained in the text. 



