Chap. Ill] 



LIGHT 



65 



quantity of chlorophyll ; even deep-lying parts normally devoid of chloro- 

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

 axes, were green. The axes were shorter than under ordinary conditions, 

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

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

 that of etiolated plants ; thus, the palisade-cells were developed either 

 feebly or scarcely at all, the fibres 

 and woody elements were quanti- 

 tatively reduced, all the cell-walls 

 were thinner, and the histological 

 structure generally was less differ- 

 entiated than in normally grown 

 plants. Even plants that were 

 discontinuously exposed to the 

 electric light showed abnormal 

 symptoms, but they bore a much 

 closer resemblance to plants 

 grown in ordinary daylight than 

 to those that were continuously 

 illuminated. The uninterrupted 

 duration of the illumination must 

 therefore be considered as the 

 essential cause of the deviations 

 from the normal structure. 



Many of these deviations may 

 be explained as being due to well- 

 known effects of light ; this is 

 especially true in regard to the 

 shortening of the axes, the more 

 intense colour of flowers, perhaps 

 also the reduced size of the leaves. 

 Other phenomena have not yet 

 been explained, such as the more 



plentiful production of chlorophyll and the simplification of the internal 

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

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

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

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

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

 grown in the extreme North possess a simpler histological differentiation 

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

 and that individuals of these species when cultivated in continuous light 

 become similar to those grown in the polar zones. 



SCH1MPER F 



Fig. 42. Firms anstriaca. Transverse section 

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

 b in continuous electric light. Magn. After Bonnier. 



