CHAPTER IV. 



PHOTOSYNTHESIS AND EESPIEATION. 



104. Questions arising from Work on Seedlings. 



The observations you have made on the growth of seedlings 

 must have raised many questions, such as the following : 

 Why does the young main root grow vertically downwards, 

 no matter how the seed is placed? Why does the shoot 

 grow upwards ? Why does a seedling remain yellow when 

 kept in darkness and ultimately die, while a seedling set in 

 the light has green leaves and keeps on growing? Is it 

 possible to make a main root turn from the vertical direc- 

 tion which it usually takes ? How does growth take place ? 

 Where, and how, is the force shown by growing roots and 

 shoots developed ? How would the growth of a young Bean 

 plant be affected if one cut off the cotyledons, or the root, 

 or the shoot? How does the seedling get food when that 

 stored in the seed is all used up ? 



The only way in which one can gain any real knowledge on 

 these points is to put each question to a living plant and 

 make the plant itself give the answer in other words, to 

 make experiments. Write down any other questions that 

 occur to you as your work proceeds. In each case keep a 

 record of (1) the inquiry, (2) methods and apparatus used, 

 (3) observations and results, (4) inferences. 



105. How do Plants Peed? After the seedling has 

 used up the food laid up for it in the seed (in the embryo 

 itself or in another part of the seed) , it must, in order to go 

 on living and growing, get food in some other way. From 

 what sources, and by what processes, does the plant obtain 

 food ? What substances does the plant need for healthy life 

 and growth? Seedlings grown in darkness lose in dry 

 weight and eventually die (Art. 65) ; the smaller the amount 

 of food stored in the seed, the shorter is the life of the 



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