MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 289 



an inhibition of this character following the exclusion of light from a 

 plant. Not only does the formation of certain important members 

 of the shoot fail to occur, but the reduction extends even to the pro- 

 toplasts, in which multiplication may go on unhindered even beyond 

 the ordinary point, but which do not undergo all of the transforma- 

 tions and differentiations characteristic of the mature plant. The 

 lack of differentiation of the tissues of the more purely mechanical 

 functions would of course be most apparent in the effects produced 

 on expanded lamellar structures, such as leaves, especially in those 

 forms in which the mechanical elements are grouped in complicated 

 anastomosing strands. On the other hand, it is to be readily seen 

 that in leaves with a parallel venation and basal growth, such as 

 those of Narcissus, the extension of the leaf does not depend to such 

 a great extent upon the completeness of the differentiation of the 

 tissues, but rather upon the continued formation of additional cells. 

 As a matter of fact such leaves may attain a size, both in width and 

 length, far beyond the normal although the tissues are by no means 

 in a normal condition of maturity. 



The same causes would be operative in the development of floral 

 organs and the formation of seeds. No plant has been found capable 

 of carrying the stamens and pistils to functional maturity in darkness. 

 Reduction or atrophy appears earliest in pollen, and the very marked 

 lack of differentiation in the tissues makes impossible the integration 

 of such a mechanically complex body as a seed in absolute etiola- 

 tions. Some diversity is to be found in the behavior of floral enve- 

 lopes however, which rest upon causes similar to those which inhibit 

 the development of complex forms and permit the formation of forms 

 of simple structure. Thus the simple spathes of the aroids may 

 reach a much more advanced stage of development than the floral 

 envelopes of Narcissus and of other plants which have two circles 

 of organs in the perianth. 



The stimulating action of light upon an organism in producing 

 morphological differentiations is not due to any direct action which 

 the rays might exert upon any particular tissue, or to the action of 

 light upon any part of the organ concerned. 



The stimulative effect of illumination, like that of many other 

 forces, may be received by one portion of the body and transmitted 

 to another, and the impulses may even be communicated to organs 

 not actually formed at the time the stimulating rays were received. 



