72 MAIZE 



Chap, hitherto dormant seed is known as germination (Figs. 15c and 



TV 



' ' 16). A seed will not germinate until it comes under the influ- 

 ence of favourable conditions, and may lie dormant for many 

 years until such conditions supervene ; these conditions vary 

 with different sorts of plants, but all include : (1) moisture ; (2) 

 heat ; and (3) sufficient air for the growing plantlet to breathe. 

 The seed of the maize plant will retain its vitality for two or 

 even three years ; but after the first year there is a marked 

 decrease in vitality, and after two years maize is considered 

 practically useless as seed ; this is independent of any question 

 of injury by weevil or grain moth, and may, perhaps, be con- 

 nected in some way with the presence of a considerable quan- 

 tity of oil in the embryo ; this oil readily turns rancid at high 

 temperatures. 



Experiments conducted at the Botanical Experiment 

 Station of the Department of Agriculture, Pretoria, show that 

 it requires from three and a half to eleven days after sowing 

 the maize-seed for the seedling to appear above the ground. 

 The difference in time of germination is largely influenced by 

 the warmth of the soil ; but it is evident that temperature is 

 not the sole controlling factor, and that associated with it is 

 the degree of moisture of the soil. Depth of planting also 

 affects germination, deep planting tending to delay it ; 

 very shallow planting (i.e. less than 2 inches) has in South 

 Africa a similar effect, perhaps because the surface soil is 

 more rapidly affected by drought. The germinating embryo 

 depends on the endosperm for its supply of food-material 

 until it has developed a root- and leaf-system (<J 63). In 

 germination the radicle grows downwards or earthwards, and 

 is therefore said to be geotropic ; the plumule upwards or 

 away from the earth, and it is therefore called apogeotropic. 



If the seed be turned upside down so that the radicle is 

 forced to commence growth upwards and the plumule to grow 

 downwards, they quickly bend round until they have regained 

 their normal positions; this is shown in Fig. 17. 



65. The Maize Seedling. — The seedling stage (Fig. 18) of 

 the maize plant is in many respects the most critical in its ex- 

 istence. While it is small it is more seriously affected by the 

 depredations of insect pests (chap. X.), and is more sensitive 

 to fluctuations in the weather conditions. It is obvious that 



