AN INTRODUCTION TO PLANT BIOLOGY 



85 



early stages of germination in seeds which 

 are germinated without contact with soil. 

 This latter is best because the particles of 

 soil cling to the seeds and make them more 

 difficult to study. 



To germinate seeds without soil, place 

 them between layers of cotton batting, 

 sphagnum moss, sawdust (some kinds are 

 too acid), blotting-paper, filter-paper, or 

 other soft papers. Keep moist, not wet, and 

 warm. Or simply place seeds on a few 

 layers of soft paper on a flat dish (such as 

 a dinner-plate) and ke p moist, warm, and 

 covered. Sand or cotton under the paper 

 will help hold moisture. 



(L) Examine various stages of bean seed- 

 lings grown without soil. Compare care- 

 fully with seedlings growing with their roots 

 in soil, and make sketches of the chief stages. 



(D) In order to determine whether any 

 part of the hypocotyl grows more rapidly 

 than others, make equidistant marks with 

 waterproof India ink, and observe changes 

 of distances between marks as growth pro- 

 ceeds (see Fig. 34). 



FIG. 34. Hypocotyl of 

 bean seedling marked to 

 show region of greatest 

 growth (between and 

 5). (From Strasburger.) 



THE WORK OF THE ORGANS OF A PLANT : AN INTRO- 

 DUCTION TO PLANT PHYSIOLOGY 



The preceding lessons have dealt largely with the structure 

 of the various parts or organs of the bean plant ; and all 

 the facts to which special attention has been given are true 

 of the vast majority of the plants which have roots, stems, 

 and leaves. In short, the bean plant has been studied as 

 a type of the plants which we most often see in everyday 

 life. In connection with the study of structure, some brief 

 mention has been made of the use or work of each organ, 

 but fuller explanations have been reserved for this section. 

 As far as possible, the following physiology lessons are 

 based upon the bean plant, but sometimes we shall use 



