120 The Waterlilies. 



about an hour later than on subsequent days, closes earlier, and spreads 

 but half as wide. An exception to this must be made for N. amazonum, 

 whose very peculiar habits are detailed in the description of the species. 

 N. rudgeana has also shown a very short nocturnal period of opening. 

 Observations on other Hydrocallis species would undoubtedly yield 

 interesting results. The characteristics of each species, so far as known, 

 are given in the taxonomic chapter. 



The stimulus to these actions is to be attributed, in diurnal species at 

 least, wholly to light. If plucked and taken into a room they rapidly close, 

 even though the normal time has not come. On the following morning, 

 however, they reopen even in a very dimly lighted room. Subsequent 

 movements of the cut flower soon become irregular, and it finally ceases to 

 move. This is" probably due to the death of the protoplasm in the sensitive 

 or motor centers, though the flower may remain open without wilting for 

 some days. That light is the normal stimulus is also shown by the earlier 

 opening of the flowers in more northern latitudes. Thus Kerner (1895) 

 gives 7 a. m. as the time for opening of N. alba at Upsala, and 8 to 9 a. m. 

 at Innsbruck, 13 farther south. Heat seems to have no effect upon the 

 Eu-castalia group in ordinary atmospheric quantities ; for the time of 

 opening and closing remains the same on days and nights when the mer- 

 cury is continually above 8o F. and on cool, cloudy days when the temper- 

 ature does not rise above 65 F. In tropical species as grown out of 

 doors in our climate heat does have a marked effect. One evening in 

 1900, when the mercury registered about 95 F., N. zanzibariensis remained 

 open nearly an hour later than usual ; and in autumn, when the night 

 temperature reaches 40 F. and the plants are looking the worse for wear, 

 the diurnal tropical species become very irregular and open but a little 

 way. The conclusion to be drawn is that the plant itself must be in a 

 certain condition of health or tonicity to enable its parts to perform their 

 functions. The effect of heat is essentially systemic rather than local. In 

 Lotos it seems likely that heat may have a more distinct influence upon 

 the flowers, but it is still obscure. They do not close until the heat of the 

 sun is making itself felt, but on exceedingly hot nights they open to 

 perfection, and on much cooler days they close at the usual time. But 

 when the cold of autumn injures the plants, they sometimes remain open 

 two or three days and nights continuously. On one occasion at Riverton, 

 N. J., I saw about sixty large flowers of this type cut in the morning and 

 placed in jars of water in a shaded glass house ; they closed very slowly 

 and incompletely. We must conclude, therefore, that light is again the 



