Physiology. 



119 



(Fig. 52) ; thus the bud maintains its erect position and is kept submerged. 

 Then in due time, the bud having matured and the peduncle having 

 reached a suitable length, the latter straightens up and lifts the former into 

 the proper position for opening. In N. flavo-virens, where I have noticed 

 this most plainly, the flower stands about a foot above the water. 



The opening of the flower occurs at a particular time of day for each 

 species of Nymphaea. Indeed, we have attempted in the accompanying 



Fig. 62. A strong-growing waterlily in shallow water. 



list * to imitate Linnaeus's floral clock in this genus alone. After remain- 

 ing open a few minutes (N. amazonum) or hours, the flower closes at a 

 certain time, and this is repeated on two (N. flavd) or three {N. odorata, 

 caerulea, etc.) to six or seven (N. gigantea) successive days. This is the 

 foundation on which was based the statement of Pliny and others that the 

 flowers retreat under water at night. The process of opening and closing 

 usually occupies nearly an hour. On its first day the flower always opens 



* Floral clock for the latitude 



8- 4 a. m. N. amazonum (new flower) opens. 

 t- 8 N. amazonum (old flower) opens wide. 



6-6 N. amazonum closes; N. marliacea car- 



nea opens. 

 6-7 N. alba candidissima and odorata minor 



open. 

 N. gracilis and elegansXzanzibariensis 

 open. 

 7- 8 N. elegans, capensis, and caeruleaXzan- 



zlbariensis open. 

 N. caerulea, marliacea chromatella, and 

 tuberosa open. 

 8-9 N. marliacea chromatella (new flower) 



opens. 

 N. capensisXzanzlbarlenBis opens. 

 8-10 N. zanzibariensisX opens. 



10-11 N. mezicana opens. 



N. rubra and rubra rosea close. 

 11-12 m. N. tetragona and zanzibariensis open. 

 N. omarana closes. 



of Philadelphia {40 N.). 



13- 1 p. m. N. odorata, tuberosa, caerulea, and ele- 

 gans close. 



N. alba candidissima closes. 



N. elegansXzanzibariensis and marliacea 

 chromatella close. 



N. mexicana closes. 



N. capensisx zanzibariensis closes. 



N. tetragona, gracilis, and Pennsylvania 

 close. 



N. capensis, zanzibariensis, and zanzi- 

 bariensisX close. 



1-2 

 2-3 



8-4, 



4-6) 



6-6 



6-7 



7- 8 



8- 9 



9-10) 

 10-lH 

 11-12 



N. dentata and omarana open. 

 N. amazonum (old flower) opens sepals. 

 N. rubra, rubra rosea, and devonlensis 

 open. 



N. rudgeana opens and closes (Casp.). 



