Chap. Ill] 



LIGHT 



65 



quantity of chlorophyll ; even deep-lying pai'ts normally devoid of chloro- 



ihyll, such as the inner cortex, the medullary rays, and the pith of woody 



ixes, were sjrccn. The axes were shorter than under ordinary conditions, 



;he leaves smaller and thicker, the flowers normally developed but more 



ntensely coloured. The internal structure (Fig. 42) strongly resembled 



hat of etiolated plants ; thus, the palisadc-cells were developed either 



cebly or scarcely at all, the tibres 



ind woody elements were quanti- /ifSP^^^^^Si^^^^^^^Bii^Sl.Q 



atively reduced, all the cell-walls vsZ 



vere thinner, and the histological 



tructure generally was less differ- 



:ntiatcd than in normally grown 



)Iants. Even plants that were 



liscontinuously exposed to the 



lectric light showed abnormal 



\-mptoms, but they bore a much 



loser resemblance to plants 



■rown in ordinary da}'light than 



those that were continuously 



luminated. The uninterrupted 



iiration of the illumination must 



lerefore be considered as the 



ssential cause of the deviations 



■cm the normal structure. 



Many of these deviations may 

 e explained as being due to well- 

 nown effects of light ; this is 

 specially true in regard to the 

 lortening of the axes, the more 

 itense colour of flowers, perhaps 

 ISO the reduced size of the leaves. 



ther phenomena have not yet 

 een explained, such as the more 



lentiful production of chlorophyll and the simplification of the internal 

 ructure. It must be shown by experiments carried on in the polar 

 3nes whether or no any significance must be attached to the fact that 

 le electric light differs somewhat in quality from daylight. In favour 

 f the opinion that we have here to deal with effects that would also hold 

 ue in the case of sunlight are the facts stated by Bonnier, that plants 

 rown in the extreme North possess a simpler histological differentiation 

 lan the same species on high mountains of Central or Southern Europe,' 

 id that individuals of these species when cultivated in continuous hghtl 

 "come similar to those grown in the polar zones. 



Fig. 42. Pimis .-lustriaca. Transverse section 

 through a needle : a in ordinary (intermittent) light, 

 d in continuous electric light. Magn. After Bonnier. 



