THE SEED: GEBMINATION 25 



fills up the entire space within the seed coats as in the case of the Pea, 

 Bean, Horse-Chestnut, Oak &c. ; or it may occupy only a very small 

 space as in Wheat, Onion &c., and remain imbedded in a substance at 

 one time called albumen, but now more generally call-fed perisperm. 



When the embryo occupies the whole seed, as in the case of the 

 Bean &c., all the reserve material for the purpose of nourishing the 

 young plant is stored up in the fleshy seed-leaves or cotyledons, and it 

 is from these that food supplies are drawn until the young root has 

 developed sufficiently to absorb food from the soil, after germination 

 has taken place. In the case of other seeds, however, like those of the 

 Wheat and Onion, the young plant is fed upon the albumen or peri- 

 sperm, and not on the seed leaves, until roots are formed. 



Germination. — Seeds germinate as the result of a certain amount 

 of heat, moisture, and air. The seeds of some plants germinate in a 

 much lower temperatxure than others, but there is a certain point called 

 the ' optimum ' at which seeds of any given plant will sprout more readily 

 than at a point below or above it. The best or ' optimum ' tempera- 

 ture for germination varies according to the nature of the plant or 

 species, and the gardener learns by experience which temperature is 

 most suitable for raising the seeds of any particular plant. He knows 

 for instance that the seeds of many plants will sprout sooner if they are 

 sown upon a hotbed than if they are sown in the open ground where 

 the temperature may be 10° or 20° lower. He also knows that a 

 certain amount of moisture is absolutely necessary, and that the free 

 circulation of air between the particles of soil shall not be impeded^ 

 as he usually takes particular care to have the soil well drained, so 

 that the water and consequently the air shall pass through it freely. 

 Speaking generally, the seeds of most of the plants described in this 

 work germinate readily either out of doors in autumn or spring ; in 

 cbld frames without artificial heat ; or in the gentle heat of a hotbed or 

 greenhouse, say 60° to 70° F. or even less. 



Heat and Cold. — When a seed ' sprouts ' or germinates as a result 

 of the suitable conditions referred to above it is obvious that growth is 

 taking place. It undergoes a change from the apparently dried condition 

 in which it was before its contact with moisture or suitable heat. In 

 fact, heat is the prime mover of life in the seed ; hence by the use of 

 hotbeds or frames or greenhouses several degrees more heat are obtained 

 than out of doors. Chemical changes take place in the seed ; water is 

 absorbed from the soil through the seed coats ; the latter are soon unable 

 to contain their swollen contents and consequently burst. The first seed- 

 leaves are pushed upwards through the soil, and the tiny rootlet down- 

 wards into it. These signs are simply an indication of the work that is 



