82 THE AMERICAN BOTANIST 



been figured and most people are familiar with its appearance, 

 but no illustrations that I can find have ever betn made of the 

 reverse side. The reason' is the difficulty of lifting from the 

 water and turning over so large a leaf — whose substance is 

 no thicker than paper and besides is armed with needlelike 

 spines — without breaking it. The photograph shows particu- 

 larly well the uni(|ue mechanism whereby the leaf gets its ex- 

 treme buoyancy and also the strength which enables it to keep 

 rigid in so unstable a medium as water. It has been stated 

 that Sir Joseph Paxton, the designer of the Crystal Palace, 

 got his idea from the study of the structure of this leaf, with 

 which, as gardener at Chatsworth — almost the first place the 

 plant was grown after its introduction — he was of course well 

 acquainted. 



"Spruce the botanist who travelled in Central America in 

 1849 and saw the plant growing in its native waters said that 

 'the leaf when turned up suggested some strange fabric of 

 cast-iron just taken out of the furnace ; its color and the 

 enormous ribs with which it is strengthened increased the 

 similarity.' The ribs which radiate from center to circum- 

 ference, though hollow have a depth of 4 to 5 inches at the 

 center and with the septae divide the whole of the under sur- 

 face into a series of chambers, air tight when the leaf is in 

 the water. As the leaf exhales air through the stomata on the 

 under side it is caught in these chambers, pushing the water 

 down just as the contained air does in a diving bell. The air 

 cham1)crs give the leaf a buoyancy more than twenty times 

 greater than it would have without them and as the leaf is 

 al)lc to increase (<r diminish the supply of air it follows that 

 It can control its buoyancy. How great a weight a leaf can 

 support was proved l)y the late Mv. W. Sowcrby, who was 

 Secretarv at the time. Placing a sheet of zinc to cover the 



