MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



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flowers, but C. DeCandolle's experiments showed that, although the 

 production of flowers was reduced in light from which the rays in 

 question had been screened, yet some were formed, so that the action 

 of ultra-violet was not indispensable to the growth and development 

 of these organs. It is not impossible that the results of both ob- 

 servers were due to the diminished intensity of all of the rays con- 

 sequent upon the experimental methods used. This seems the more 

 probable since the sporangia of Pilohohis and other fungi are capable 

 of normal development in the absence of the ultra-violet rays. In a 

 lengthy examination of the influence of the principal divisions of 

 the spectrum Teodoresco found that the development and differentia- 

 tion of the tissues of the leaves and stems was most nearly like that 

 of etiolated plants in green light, more nearly perfected in red and 

 that these organs were most highly developed in blue-violet rays. 

 These results however, are not capable of any simple interpretation 

 since the phenomena obtained by exposure of a shoot to any restricted 

 portion of the spectrum must be complicated by the intervention of 

 the specific absorption of the rays by chlorophyl, and also by the heat 

 of the rays used. It is, of course, not improbable that the more re- 

 frangible rays may exert a stronger morphogenetic stimulation in the 

 same manner that they have the greatest phototropic influence of any 

 portion of the spectrum. Outside of these considerations it is to be 

 noted that the development and differentiation of any tissue is more 

 or less dependent upon the functional activities devolving upon it. 

 The removal of any condition incident to the proper performance of 

 a function, inhibiting the function itself may result in the atrophy, 

 partial or complete, of the organs concerned. Leaves are examples 

 which illustrate this regulatory device most clearly. The capacity of 

 the plant for cutting off mature foliar organs which have been rendered 

 functionless by any cause is well known and has long been recog- 

 nized. Both phases of this relation are exhibited in the tests which 

 have been made with the growth of shoots in atmospheres lacking 

 carbon dioxide. In such experiments in which plants are used that 

 are furnished with reserve food, the leaves and stems make a rapid 

 growth with lessened differentiation owing to the inhibition of the 

 photosynthetic function, while mature leaves already formed are cast 

 off as a result of their uselessness. The amount of action shown 

 by young leaves cultivated in atmospheres lacking carbon dioxide 

 has been expressed in one of my contributions to this subject as fol- 



