CHAPTER XVII. 



GROWTH. 



174. Meaning of growth. By growth is usually meant an 

 increase in the bulk of the plant accompanied generally by an 

 increase in plant substance. Among the lower plants growth 

 is easily studied in some of the fungi. 



175. Growth of roots. For the study of the growth of roots 

 we may take any one of many different plants. The seedlings 

 of such plants as peas, beans, corn, squash, pumpkin, etc., 

 serve excellently for this purpose. 



Exercise 36. 



176. To study growth of roots. The seeds, a handful or so, are soaked 

 in water for about 12 hours, and then placed between layers of paper or 

 between the folds of cloth, which must be kept quite moist but not very wet, 

 and should be kept in a warm place. (See demonstration 2.) 



The primary or first root (radicle) of the embryo pushes its way out 

 between the seed coats at the small end. When the seeds are well germi- 

 nated, select several which have the root 4-5 cm long. With a crow-quill 

 pen we may now mark the terminal portion of the root off into very short 

 sections as in fig. 81. The first mark should be not more than \mm from 

 the tip, and the others not more than imm apart. Now place the seedlings 

 down on damp filter paper, and cover with a bell jar so that they will re- 

 main moist, and if the season is cold place them in a warm room. At 

 intervals of 8 or 10 hours, if convenient, observe them and note the further 

 growth of the root. Sketch the root with the marks at the beginning of the 

 experiment, and at the different times the observations are taken. Where 

 does the elongation take place ? Determine this by the marks on the root 

 which separate. Where is the region of greatest elongation ? Does the 

 region of greatest elongation change ? 



102 



