MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



297 



a very unsymmetrical appearance. Polystichnm acrostichoides de- 

 veloped etiolated upright leaves with the pinnae retained in tightly 

 rolled clumps, and when these organs were illuminated the pinnae 

 made a development which did not carry them far enough to consti- 

 tute normal structure, while the rachis made a pronounced curva- 

 ture below the lowermost pinnae in such manner that the upper por- 

 tion of the leaf was held in a position fairly horizontal. 



The positions assumed by such etiolated organs after illumination 

 have been held by Detmer to be due to -photo-epinasty and photo- 

 hyponasty (see p. 14), or to special relations of the rate of growth of 

 the opposite flanks of dorsiventral organs induced by illumination. 



Fiai 



Fig. 174. Ervum Lens, i, specimen cultivated in normal illumination; 2, plant 

 cultivated in darkness five days, then illuminated ; 3, plant cultivated in darkness eight 

 days, then illuminated ; 4, plant cultivated in darkness thirteen days, then illuminated ; 

 5, etiolated plant. After Ricome. 



So far as leaves are concerned the movements in question are such 

 as to carry the laminae to a normal position, but in the case of the 

 foliar hood of the spathe of Arisacma it has been seen to place this 

 structure in an extraordinary recurved position in which it must be 

 wholly useless as a floral organ. While it seems entirely clear that 

 the comparative rates of growth of the two halves of a dorsiventral 

 organ may be radically modified by illumination, yet the action in 

 question is a general one, and does not necessarily entail any special 



