406 



PHYSIOLOGY OF GROWTH. 



offer excellent material for observation. In many monocotyledons 

 (Zea, Triticnm) we find on investigation that the leaves of seed- 

 lings grown in continuous darkness, as compared with leaves of 

 the same age which have developed in the light, attain a consider- 

 able length, but remain narrow. 1 



FIG. 134. Aerial part of a 

 seedling of Phaseolus grown 

 in the dark. 



FIG. 135. Aerial part of a seedling of Phaseolus grown 

 under normal conditions. 



It is of interest that not only do plants grown under ordinary 

 illumination on the one hand, and in complete darkness on the 

 other, exhibit considerable differences in their entire development, 

 but that similar differences also clearly appear in the cultivation 

 of plants in light of greater and less intensity. 2 To demonstrate 

 this I have employed wooden boxes 55 cm. high and of about 680 

 sq. cm. area of base for the reception of the culture vessels and 



