144 RELATIONS OF PLANTS TO LIGHT 



a weak diffuse light penetrates, and keep under proper cultural 

 conditions for a month. Care must be taken to maintain the 

 plants in healthy green condition, since the reaction is in no sense 

 an etiolative one. The main shoot bearing flower buds will prob- 

 ably not develop anything but normal upper leaves, but the lateral 

 branches of the shaded specimens will show rounded leaves of 

 the types usually formed at the bases of the stem. 



77 78 



FIG. 77. Cassia at noonday with intense illumination and high temperature. 

 FIG. 78. Cassia (see Fig. 75) showing position of leaves at 6 P. M. (sunset) in 

 warm room. 



218. Influence of Light on the Formation of Tubers. The 



thickenings of the stolons arising from the basal portions of the 

 main axes of plants of Solanum tuberosum (potato) form the well 

 known potatoes. These formations generally arise only in 

 organs from which the light is excluded, although known to oc- 

 cur in plants growing closely crowded together and hence shaded 

 from intense light. Fill a few flower pots completely full of 



