1^S2 LIVING PLANTS 



in weak sugar solutions in strong light 

 formed anthocyan, while other specimens in 

 water and exposed to diffuse light did not, 

 showing that the color is formed when needed 

 only, and not accidentally, although its oc- 

 currence as in underground organs or in the 

 center of massive tissues must be accidental 

 and not useful. 



Anthocyan as a screen is not always con- 

 fined to the upper layers of the leaf. The 

 leaves of the banana (Musa) are vertical and 

 rolled up with the ventral stirfaces outermost 

 when young. One species develops color on 

 the under side, which disappears as the leaf 

 unrolls and comes down to a horizontal posi- 

 tion. Uncaria, Alpina, Belemcanda, and other 

 plants afford similar instances. The pinnules 

 of Mimosa pudica are provided with a red- 

 dish coloring matter in the surfaces of the 

 lower sides which are exposed when closed 

 together in the ''hot sun" position. 



The coloring matter in the pistils of anemo- 

 philous plants such as Populus, Salix, Plata- 

 nus, Ulmus, Ostrya,Carpinus, Corylus, Alnus, 

 Acer, Fraxinus, Rumex, and others in which 

 it can have no possible significance for animals, 

 also serves as a screen against the effects of 

 light. The growth of the pollen tube down 

 through the pistil would be very much hindered 



