36 



SEEDS AND SEEDLINGS. 



which the seeds are planted by inverting over it a large flower-pot or 

 putting it into a tin or wooden box with a few holes for ventilation. 

 Compare the rate of growth of the two sets of seedlings from day to 

 day, and note any other differences between them. See Art. 128. 



63. Conditions necessary for Germination. If you 



have carefully carried out the simple experiments on germi- 

 nation for which directions have been given, you will know 

 what conditions are essential for germination of a seed 

 which contains a live but dormant plantlet. Water, oxygen, 

 and sufficient heat are the three essentials for the awakening 

 of the young plant from its sleep. We shall see later that 

 for the continued healthy growth of the plant other things 

 are necessary, without which the seedling after a time dies. 



64. Growth in Light and in Darkness. If you have 



carefully performed the sim- 

 ple experiments mentioned 

 in Arts. 56 and 57, you will 

 see on reflection that the 

 germinating seed must lose 

 carbon in its respiration. 

 To measure this loss we 

 must, of course, dry the 

 seeds and seedlings before 

 weighing them. Does this 

 loss occur both in light and 

 in darkness ? 



* (a) Take about forty Beans as 

 nearly alike in size and weight 

 as possible ; select four of them 

 as samples, and find their weight 

 after thoroughly drying them on 

 a water- or sand-bath or in a 

 slow oven. Take the dry weight 

 of a seed, found in this way, as 

 the average. Sow half of the 

 seeds in sifted garden soil in a box 

 which is kept in darkness, the other 

 half in a box kept in full light ; 

 water both lots about equally. 



At the end of each week measure and record the average height of the 

 shoot in each lot of seedlings ; remove three seedlings from each box, 



Weeks 



Fig. 21. Chart on which to plot the 

 Curves of Height and Weight. 



