Growth. 



25 



leaves of Calla or C aladium into intervals, as in the previous 

 experiments, and make_dailvj neasurements to determine th e 

 zone ot maximum growth and the_dail>ua.te. Does the petiole 

 elongatejijtHFiame^rate in alLslage^ of its de velopment ? 



14. Growth of roots. — Germinate seeds of pea {Hsum), 

 bean [Phaseolus), or squash 

 ( Cucurbita) in fine, moist, clean 

 sawdust, until the main- roots 

 are two to three centimeters in 

 length. Remove, and wash free 

 from adhering particles, select- 

 ing six of the most vigorous 

 specimens with straight roots. 

 Lay each seedling in turn on a 

 strip of moist filter paper, on a 

 table, against the end of a ruler, 

 with the root extending along 

 the top of the ruler. Use the 

 wire-and- thread inking device 

 described above, and mark the 

 roots into intervals of i mm. 

 Allow the ink to harden, dip the 

 seedlings in water, and replace 

 in the sawdust, with the roots de- 

 pending vertically ; place in a 

 room kept at a temperature be- 

 tween 16° and 22° C. Take up 

 two of the seedlings a day later, 

 and lay on a table, in the same 

 position with a ruler as before, making exact measurements of the 

 distances between the marks. Take up two more on the follow- 

 ing day, and measure. Take up the third lot on the third day, and 

 make measurements. Find the total amount of growth in each 

 root, and ascertain the location of the region of greatest growth. 



Fig. II. — Seedling of pea with the 

 root marked into centimeter intervals, 

 and the same 24 hours later, showing 

 the location of the zone of maximum 

 growth. After Sachs. 



