70 



EXPERIMENTAL PLANT PHYSIOLOGY. 



Fig. 65. 



EXPERIMENT 87. 



MEASUREMENT OF ROOT EXTENSION. 



Germinate Pea, Bean, or Squash seeds until the primary roots 

 are 2 cm. in length. Place one of the seed- 

 lings in the bowl of a thistle-tube or small 

 funnel, with the root depending downward in 

 the tube. Cover the seedling with moist 

 cotton and place the bottom of the tube, in 

 a vessel of water. By means of India ink 

 mark off intervals of 2 mm. on the tube, and 

 set the whole apparatus in equal-sided light 

 so far as possible. Note the position of the 

 root-tip at least twice daily. A growth of 4 

 to 20 rnm. in a day may be expected. 



Focus a horizontal microscope with a 

 power of 25 diameters on the extreme tip of 

 the root. It will be seen to move slowly 

 across the field of view. (Fig. 65.) 



EXPERIMENT 88. 



MEASUREMENT OF GROWTH INCREASE BY WEIGHT. 



Select a young Squash or Pumpkin which 

 has attained a diameter of a few centi- 

 meters and place on the pan of a druggists' 

 balance (Fig. 24), with the vine supported in 

 such a manner that it bears as little weight as 

 possible on the balance. Place in the second 

 pan sufficient weights to establish an equilib- 

 rium. Equalize the scale morning, noon, 

 and evening, and the amount of increase may 

 be directly obtained. During the period of 

 most rapid growth the daily increase will 

 amount to 200 to 700 grams. At times the 



Seedling of Squash in a .^veight of the fruits will be found less at 

 thistle-tube. (Detmer.) , . . . . ^ 



noon than m the morning owing to excessive 



evaporation of water from its surface and that of the leaves. 



53. Grand Period of Growth. — With regard to growth three 

 regions may be observed in any organ composed of many 

 cells : one in which new cells are constantly forming, as in 

 the tips of roots and shoots ; another in which the cells are in- 



