102 PL4NT PHYSIOLOGY. 



Brown, H. T. Vice-Presidential address in Nature, 60, 474. 

 Kohl, F. G. Die assimilatorische Energie der blauen und 



violetten Strahlen des Spektrums. Berichte der deutschen 



botanischen Gesellschaft, 15, 361, particularly the plate 



XVI. 

 On synthesis of albuminous substances, see note in Nature, 



58, 368. 

 Progress of Agricultural Chemistry. Nature, 61, 116. 



Section 2. Growth. 



A. Increase in Size. 



65. What is the approximate rate of growth in length of a 

 vigorous shoot under normal conditions, and what fluctuations 

 does it show? 



Answer by Experiment 33. 



EXPERIMENT 33. This may be tested by placing the tip of a 

 rapidly-growing shoot, such as a flower-stalk, in connection with a 

 self-recording mechanism whose records may be compared with 

 records of temperature and other external conditions. Prepare an 

 autographic auxanometer like that of Fig. 24, consisting essentially 

 of a recording cylinder and a magnifying-wheel. From a Waterbury 

 dollar alarmless clock of four inches diameter remove glass, face, 

 hands, and all surplus works, leaving the central steel spindle pro- 

 jecting some 20 mm. above the brass frame of the works. Have 

 turned on a lathe a hard-wood (maple is excellent) cylinder 30 cm. 

 (a foot) long and 25 mm. (an inch) in diameter, with holes at each 

 end a trifle smaller than the clock-spindle and exactly centered by 

 the lathe, so that the cylinder may be forced gently down upon the 

 spindle and revolve exactly vertically above the clock, on which it 

 will turn once an hour. Cover the cylinder with the smoothest ob- 

 tainable paper (if highly glazed paper is used, it will go on without 

 wrinkles, but an unglazed paper will fit better if put on wet), fasten- 

 ing it by mucilage along the free edge, which must turn in a direc- 

 tion not to catch the pen as the cylinder revolves. Have turned on 

 a lathe (from maple) a magnifying-wheel, forming four concentric 

 wheels of different sizes side by side in one piece (Fig. 25), the 

 outer 12 cm., the next 6 cm., the next 3 cm., and the smallest 1.5 

 cm. in diameter. All are to be as thin as they can be turned, and 

 grooved on their rims. A very small hole, a little larger than a 

 coarse needle, is to be turned exactly in their common axis, and the 



