i9i3' I 9 I 4-] Plant Growth-Rhythms. ioi 



the spring, summer, autumn, and winter phases. Other plants 

 in Java again foliate and defoliate independently of the 

 external conditions, and this takes place at different times in 

 plants growing in contiguity, evidencing that each individual 

 has its own autonomic and not induced annual rhythm. 



2. Daily Peeiodicity. — In the course of the day of 

 twenty - four hours there is considerable variation in the 

 external conditions, — the alternation of light and darkness, 

 accompanied by changes in temperature, humidity, and other 

 atmospheric conditions. What is the influence of the sum 

 of these conditions on daily growth ? This question can be 

 answered by experiment. 



Apparatus and Methods of recording Groivth. — The first 

 recorded experiment on the longitudinal growth of shoots is 

 that of Stephen Hales, the founder of modern experimental 

 physiology ('Vegetable Statics,' p. 331, Plate 18). Hales' 

 apparatus was of the simplest, consisting of a stick with a 

 number of pins fixed in it at intervals of a quarter of an inch. 

 Dipping the pin points in red-lead and oil he marked a young 

 vine shoot, and then measured the increase of the intervals 

 after the lapse of some time. For demonstration purposes 

 this method is still useful. Other devices are direct measure- 

 ment of the object by means of a millimetre scale fixed 

 alongside and some form of simple auxanometer, such as that 

 described in ' Proc. Scot. Mic. Soc.,' 1908, vol. v. pp. 66-69. 

 The growth of roots may be measured by enclosing the root 

 in a vertical graduated tube filled with water, and taking 

 readings from time to time. For accurate research an auto- 

 matic recording auxanometer is necessary, by means of which 

 continuous records for long periods can be obtained. 



The first elaborate researches on Periodicity are those of 

 Sachs (Arb. Bot. Inst., Wurzburg, 1874, Bd. 1, pp. 99 et seq.) 

 and Baranetzsky (Mem. Acad. Imp., Petersburg, 1879, 7 Ser., 

 vol. xxvii. pp. 1 et seq.). Sachs was the inventor of the 

 auxanometer, and was the first to demonstrate clearly the 

 daily periodicity. He showed that it. was affected not by 

 light variation alone but by all the accompanying environ- 

 mental conditions. Baranetzsky improved the apparatus and 

 extended the research. Both investigators worked with 

 shoots artificially subjected to an alternation of twelve hours' 



