SEEDS AND SEEDLINGS. 



35 



ensures the highest percentage of plants from the seeds 

 sown. The temperature below which germination does not 

 occur is called the minimum, that above which there is no 

 germination is the maximum, while the most favourable 

 temperature is the optimum ; these might be called respec- 

 tively the lowest, highest, and best temperatures for germina- 

 tion. In general, the temperatures at which the seeds of most 

 cultivated plants (excluding, of course, hot-house plants) 

 grow best in our climate lie between 18 C. and 35 0., with 

 an average about 24 C. 



Wheat and mustard begin to germinate at 4 or 5 C., Scarlet 

 Runner and Maize at 8 or 9 C., Vegetable Marrow (Pumpkin) at 13 C. , 

 and Cucumber at 16 C. Here are the approximate optimum tempera- 

 tures for germination of some common plants : Barley, Pea, Sweet Pea, 

 Phlox, 18 C. ; Cabbage, Carrot, Lettuce, Oats, Stock, Petunia, 21 C. ; 

 Rye, Beet, 24 C. ; Clovers, Tomato, Mignonette, Pansy, 27 C. 



(a) Place some soaked seeds in a glass jar and cover them with moist 

 sawdust ; plunge the jar into a box containing pieces of ice, which must 

 be renewed as they melt. The ice will last longer if the box contain- 

 ing it is set into a larger box, and the space between the two boxes is 

 packed with dry sawdust (why?). 



(b) Another method is to use two boxes as in the preceding, but to 

 place in the smaller box a single box of ice, with dry sawdust below 

 and around it ; place the seeds directly on the ice and cover them with 

 dry sawdust, which will be kept moist by the melting ice. 



* (c) In winter and spring the minimum temperature for germination 

 should be determined for as many seeds as possible. Into a large 

 flower-pot or seed-pan put some bits of broken earthenware at bottom, 

 and fill up the rest of the pot with sifted soil. Plant in the pot a few 

 seeds of different kinds, and bury the bulb of a thermometer at the 

 depth of the seeds, tying the thermometer stem to a stick thrust into 

 the soil. Sink the pot up to its rim in the soil of a garden bed and 

 record the temperature each day, looking for any signs of germination. 

 After two or three weeks bring the plants indoors ; keep the soil moist ; 

 make notes of your observations. Other pots should be kept in 

 different parts of the house or school, in addition to those kept outside. 

 Such experiments will show that warmth hastens germination, while 

 cold retards it. 



62. Is Light required for Germination? This ques- 

 tion is very easy to answer by experiment. 



(a) Place in a dark cupboard or cellar some jars or boxes containing 

 seeds planted in moist sawdust. Compare with seeds of the same 

 kind, planted and watered in the same way, but set in the light. 



(b) A better plan is to keep the two sets of seedlings close together ; 

 exclude the light from one lot by covering the jar or small pot in 



