486 Darwin.— On the Growth of 
8. There is no evidence that the change from night to 
daylight or vice versa has any effect per se. 
9. The curve of growth shows a minimum in the afternoon 
followed by a rapid rise towards evening. 
10. The evening rise is followed by a fall in the curve as 
the night proceeds. 
11. The rate of growth is more uniform by night than 
by day. 
It would be of interest to inquire how far the facts here 
recorded find a parallel in the growth of internodes ; but to 
this point I can only refer in the briefest manner. 
Mulder, as quoted by Sachs 1 , observed the growth of the 
leaf of Urania speciosa : Sachs points out that Mulder’s records 
give a remarkable opposition between the curves of growth 
and temperature, — one sinking as the other rises. This is 
paralleled by my observations on the change of weight in 
the fruit of Cucurbita , and is no doubt a reflection of a similar 
change in conditions, i. e. variation in the relative humidity of 
the air. 
Sachs also gives 2 the results obtained by W. deVriese in 
1847. The flower-stem of Agave americana was found to 
show either a complete cessation of growth, or an actual 
shortening, during the morning. Here again the phenomenon 
clearly depended on the relative distribution of water in the 
leaves and stem. Thus on two occasions, when owing to 
clouds or rain the transpiration must have been small, a small 
amount of growth took place in the morning. More recently 
Godlewski 3 has shown that in the epicotyl of Phaseolus any 
great diminution in the dampness of the air produces a sudden 
but temporary slowing in growth, while a temporary rise in 
growth-rate follows an increase in humidity. In some of my 
experiments this temporariness of the effect of changes in the 
hygroscopic condition of the air has been clearly marked. 
1 Arbeiten, i. p. 174. 2 loc. cit. p. 183. 
3 Anzeiger der Akad. zu Krakau, 1890. I quote from the Bot. Centralblatt, 
47» P- 307- 
