ETIOLATED SEEDLINGS 



"5 



all instances. The etiolated specimens must not be exposed 

 to intense light even for a few minutes and the examination of 

 them should be made by the use of an ordinary candle. The 

 temperature should be kept at 1 5-20° C, and not so much water 

 will be needed as in plants grown in daylight, owing to the les- 



—D. 



:-C. 



— B. 



:-a. 



Fig. 52. Cross section of portion of normal stem of young Quercus. A, proto- 

 xylem. B, median part of wood-ring in which the medullary rays may be seen. C, 

 cambium. D, bast. E, inner periderm. 



sened transpiration. Control specimens should be grown under 

 similar conditions but in full exposure to direct sunlight. 



Compare the etiolated and normal stems with regard to the 

 length and thickness of the stems, length and number of inter- 

 nodes, number and size of the leaves, and structure of all the 



