Minnesota Plant Life. 



265 



but rise above it. Besides, the leaves of the water-shield are 

 oval and not more than four inches in length, while those of 

 the lotus are circular and much larger. Water-shield flowers 

 are purple, less than an inch in diameter, and the whole plant 

 is easily distinguished from any other kind of water vegetation 

 that might be mistaken for it by a very abundant deposit of 

 transparent jelly over the stems, buds, flower pedicels and the 

 under sides of the leaves. The leaves are commonly purple 



Fig. 12.5. Water-lilie.s. After photograph by Williams. 



below and dark green, shaded with purple above. The i)res- 

 ence of the purple dye on the under sides of floating leaves 

 is not uncommon. It will be found to some extent in water- 

 lily and pond-lily leaves and in the leaves of the floating pond- 

 weed. The purple substance is a heat-producing color, and 

 apparently such sunlight as the plant does not utilize in starch- 

 making may be converted into heat by the lower layers of the 

 leaf and employed as a source of energy in various growth- 

 processes of the plant. The stem of the water-shield is some- 



