CH. Il] ETIOLATION. SUN- AND SHADE-LEAVES. 57 



cording to our experience success is by no means certain. 

 Another jar may be used for Gris'^ experiment, which 

 consists in painting a leaf with very dilute ferric chloride 

 solution. Here again it is not easy to insure success. 



(72) Form of etiolated plants^'. 



For a thorough study of the changes of form and 

 structure which accompany etiolation it would be neces- 

 sary to grow a great variety of plants. The best for the 

 purpose are plants produced from tubers or bulbs, or from 

 large seeds full of reserve material, since here the effects 

 of darkness in producing starvation do not complicate the 

 result. Among Dicotyledons, Dahlia, Helianthus tuber osus, 

 Humidus lupulus, and Beans (Faha and Phaseolus) may 

 be grown. Among Monocotyledons, any of the cereals, 

 Narcissus and Crocus. 



In each case control plants of the same species must 

 be grown in light. Compare the two sets as to develop- 

 ment of leaf, measured in length and breadth; length and 

 diameter of stem, and length of internode. 



(73) Sun- and shade-leaves. 



To see the remarkable structural characters described 

 by Stahl^, the leaves of the beech (Fagus) will serve. 

 Transverse sections must be cut from leaves which have 

 grown (1) in the fullest sunshine, and (2) in deep shade. 

 The chief point to note is the difference in the palisade 

 tissue. 



1 For an account of the experiments of Gris see Sachs' Physiologie 

 (French Trans.), p. 159. Also Sachs' Arheiten, in. p. 433, for Chlorosis. 



2 Sachs' Bot. Zeitung, 1863. 



3 Bot. Zeitung, 1880. 



