GEilMINATION. 



65 



well in the sprouting of a seed as in the hatching of an egg. 

 The proper degree of temperature for our own climate may be 

 stated at 60 to 80. Extremes 

 of heat and of cold are not, 

 however, fatal to all germina- 

 tion. In one of the Geysers 

 of Iceland, which was hot 

 enough to boil an ecror in four 



^ OO 



minutes, a species of Chara was 

 found in a growing and fruitful 

 state. The hot springs and 

 pools of San Bernardino, Cali- 

 fornia, at the constant heat of 

 190, have several species of 

 plants growing within their wa- 

 ters. Many species also arise 

 and flower in the snows of Mt. 

 Hood, along their lower bor- 

 ders. Darkness is favorable 

 to germination, as proved by 

 experiment, but not an indis- 

 pensable condition. Hence, 



while the seed should be covered, for the sake of the moisture 

 and shade, the covering should be thin and light, for the sake 

 of a free access to air. 



196. The cause of the downward tendency of the root is a theme of much discussion. 

 Some have referred it to the principle of gravitation ; others to its supposed aversion to 

 light. But it is a simple and satisfactory explanation that its growth or cell-development 

 takes place most readily on the moist side of its growing-point, and consequently in a 

 downward direction, so long as the soil in contact with its lower surface is more moist 

 than that above. Hence, also, the well-known tendency of roots toward springs and 

 water-courses. 



Review. 188. Define the term Germination. 189. Where and when to observe the pro- 

 cess. How at other seasons. 190. Prerequisites to germination. Depth of planting. 

 What chansre in the material of the seed ? State of the embryo in 225 ? In 226 ? In figs. 

 227-230 ? 11)1. What becomes of the radicle ? Of the cotyledons ? How does the plumiile 

 develop ? Show by the figures. In what plants do the cotyledons remain stationary ? 

 193. Show how the Monocotyledons germinate, by figs. 231, 232. 195. Three conditions 

 requisite. Why is moisture needed? Why air? Whence comes the sugar ? 195. What 

 degrees of warmth ? Some strange exceptions. 196. Why the root grows downward. 



' 5 



231, 232, Germination of Indian Corn. 



