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the petiole being measured in diameter and length at the same time, so 

 that there would be exactly the same conditions alfecting the growth of 

 the two dimensions. The plant was placed at a north window, and, while 

 not receiving direct sunlight, had abundant light ; the pot containing it 

 was set in a saucer kept filled with water, thus providing a constant supply 

 of moisture. The purpose was to keep the plant, as nearly as possible, 

 under normal conditions while being measured. 



The measurements of length show that a constant growth takes place, 

 there being two periods in most cases during the 24 hours in which the 

 growth was much greater than at other times, the maximum period of 

 growth occuring from 12 o'clock midnight to 8:00 a. m., the lesser great 

 period, where occurring, being in the evening. The growth in thickness 

 was constant from day to day, as can be seen from the curves, but there 

 were times during the 24 hours in which a contraction took place. The 

 measurements, in every case, show that the diameter would increase 

 gradually until a maximum point was reached, then diminish gradually, 

 but not the entire amount that it had increased, thus proving that the 

 increase in diameter was due to both growth and tension combined. The 

 amount of growth is estimated for 24 hours by subtracting the sum of the 

 increments of contraction from the total increase, thus leaving the sum 

 of the increments of increase of the organ due to actual growth. 



The measurements show that there were invariably two points of greater 

 growth, the maximum occurring between 12 midnight and !i;00 a. m., this 

 being the same time as the maximum period of growth in length occurs ; 

 the lesser great period occurring from 1:00 to 11:00 p. m. 



These show a wider range in the occurrence of the greater and lesser 

 points of growth than is found in woody stems, but is probably due to the 

 nature of the atructure of Richardia, which allows a ready response to var- 

 iations in tension. This ready response was also shown by withholding 

 water from the plant until the leaves become flaccid, then giving an abund- 

 ant supply, when the leaves became turgid in about a half hour. 



The curves show that the plant responds in expansion to an increase in 

 temperature, though in two cases where the temperature went to 34° and 

 35° C. a contraction followed in one case, and a very slow growth in the 

 other, seeming to indicate that a temperature of that extent was detri- 

 mental to the growth of the plant. This point would, of course, have to 

 be worked out much more fully before anything positive could be deduced. 



Theoretically growth in length and thickness should have their maxim- 



