114 RELATIONS OF PLANTS TO LIGHT 



variations of irritable properties in the greater majority of species 

 which form chlorophyl screens for the absorption of energy from 

 light. These deviations consist in the suppression or enlargement 

 of leaves, the attenuation of stems, the lack of differentiation of 

 embryonic tissues, the suppression of branching, and various 

 changes in the position and development of the secondaiy repro- 

 ductive organs. Fertilization and development of seeds and fruits 

 may or may not occur, according to the amount of development 

 ordinarily attained by the flower before emerging from the bud. 

 The absence of the directive stimulation of light permits organs to 

 assume positions in response to geotropism alone, or to hyponasty 

 or epinasty. Some forms of irritability, such as lateral geotro- 

 pism and phototropism may be lost, and the entire system of 

 correlations by which a plant determines the relative positions of 

 its various organs may be altered. 1 These reactions are in the 

 main adaptive efforts on the part of the plant for the purpose of 

 raising the chlorophyl-bearing organs past an obstruction inter- 

 cepting light. The growth of a plant devoid of reserve food- 

 material in darkness also entails starvation. Simple etiolation 

 phenomena should therefore be studied in branches of a shoot 

 extended into a dark chamber, or in specimens placed in darkness 

 having a supply of stored, food in the seed-leaves or tubers. 



175. Etiolated Seedlings. Place a number of germinating beans, 

 hickory nuts, acorns, or dates in a dark chamber under ordinary 

 conditions of culture, and allow them to reach the full limit of 

 growth, which will need several days, or even a few months in the 

 case of the larger seedlings. The dark room should be provided 

 with double doors tightly fitted to exclude light after the manner 

 of a photographic dark room. If this can not be procured use 

 an ordinary room with all cracks and. windows closed and dark- 

 ened and enter it only at night. Small portable dark chambers 

 of suitable size may be made of wood or sheet zinc set on a table 

 covered with sand. Suitable ventilation must be provided in 



1 Vochting, H. Ueber den Einfluss des Lichtes auf die Gestaltung, und die Anlage 

 der Bliithen. Jahrb. Wiss. Bot. 25 . 149. 1893. 



