No. 438-] 



NOTES AND LITERATURE. 



435 



As might be expected such an exhaustive investigation of the 

 relations of plants to light and darkness, leads to new and interesting 

 conceptions as to the action of illumination in determining the growth 



of the work centers. As a record of careful and interesting observa- 

 tions the first and major part of the work is of great value, but with- 

 out entering too greatly into detail, it is impossible to give a fair idea 



passing, the following plants, unusual at least from the standpoint of 



Dur., Bowka volubilis HaL, Cocos nucifera jLrvUUa somm 



In discussing the theories, hitherto presented, the author points 

 out how inadequate and unsatisfactory the explanations of etiolation 

 phenomena have been. Under the heading " Morphogenic Influ- 

 ences of Light and Darkness" the author expresses his own under- 

 standing of the problem by a careful analysis of the facts, and the 

 following is intended to give the substance of his discussion. 



Etiolation is not to be regarded as an adaptive modification on the 

 part of the plant, and the form that it assumes in darkness is not due 

 to an effort to reach the light. The various phenomena of etiolation 

 are of course, in the first instance, due to the absence of light, but it is . 

 only in some cases that a beneficial modification results. Aside from 

 the absence of chlorophyll, the basal fact connected with the condi- 

 tion of etiolated organs is that their tissues do not show the same 

 degree of morphological differentiation as do those of the normal. 

 This lack of differentiation, and the abnormal increase in size which 

 accompanies it, is most noticeable in the large parenchymatous tracts 

 of tissue. An incomplete deposition of aplastic material allows of a 

 much longer growth period. In this connection the author points 



additional parenchymal cells we have the familiar elongation and 

 enlargement of etiolation, whereas in cases like those of dorsiventral 

 leaves, where the mechanical elements are prerequisite for the expan- 

 sion of the lamina, the organ remains small. A comparison of nor- 

 mal and etiolated plants shows that growth and differentiation are 

 not only independent phenomena, but are easily separable. 



From this point of view then the phenomena of etiolation rests 

 upon the absence of the morphogenetic influence of light, or rather 

 as the author modifies it in considering the effect of continuous illu- 

 mination in producing partially elongated forms, we may suppose that 



