GROWTH. 77 



culture was first examined, we can now see that they remain 

 practically the same distance from the gonidium as when they 

 were first formed. That is, the older portions of the mycelium 

 do not elongate. Growth in length of the mycelium is confined 

 to the ends of the threads. 



183. Protoplasm increases by assimilation of nutrient 

 substances. As the plant increases in bulk we note that there 

 is an increase in the protoplasm, for the protoplasm is very 

 easily detected in these cultures of mucor. This increase in the 

 quantity of the protoplasm has come about by the assimilation 

 of the nutrient substance, which the plant has absorbed. The 

 increase in the protoplasm, or the formation of additional plant 

 substance, is another phenomenon of growth quite different from 

 that of elongation, or increase in bulk. 



184. 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. 



185. Roots of the pumpkin. 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. 

 A shallow crockery plate, with the seeds lying on wet filter paper, 

 and covered with additional filter paper, or with a bell jar, an- 

 swers the purpose well. . 



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 germinated, select several which have the root ^-$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. 66. The first mark 

 should be not more than imm 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 farther growth of the root. 



