Ill] FLOATING LEAVES 31 



covered in any spot where Waterlilies abound. In the case of 

 Nymphaea and Casialia^ a place in the sun is secured through 

 the pHabiUty of the petioles, which vary in length according 

 to the depth of the water, but do not rigidly determine the 

 position of the lamina. The variation in length of the peduncles 

 goes hand in hand with that of the petioles. The present writer 

 has measured a peduncle of Castalia alba over six feet in length, 

 and such length is by no means uncommon; Fig. 15 shows the 

 proportion borne by peduncle to flower in this case, the peduncle 

 being represented coiled in 

 order to include its entire 

 length in the sketch. It is 

 rather curious that in the 

 gigantic Victoria regia this 

 great elongation of the peti- 

 oles and peduncles does not 

 occur; the plant flourishes 

 in the shallows and has been 

 recorded in the Amazon 

 region in water only two 

 feet deepi. 



Another result of the 

 length and flexibility of the 

 leaf-stalk in the Waterlilies 

 is that the lamina can re- 

 spond freely to the move- 

 ment of the water and is 

 hence less liable to be sub- 

 merged. This response is 

 also shown in many other 

 plants which are rooled at 

 the bottom of the water 

 and bear floating leaves. Potamogeton natans'^ is a good example. 

 Here the axis from which the leaves arise, instead of being a 

 solid rhizome lying in or on the mud, as in the Waterlilies, 

 1 Spruce, R. (1908). 2 jahn, E. (1897). 



Fig. 15. Castalia alba, Greene. Peduncle 

 and flower-bud to show great proportionate 

 length of peduncle. The peduncle, which was 

 more than 6 feet long, is represented coiled 

 in order to include its whole length in the 

 diagram. (Reduced.) May 30. 191 1. [A. A.] 



