168 



LIGHT AND PROTOPLASM 



[Cii. VII 



per minute by the submerged, illuminated plant. As is shown 

 in Fig. 45, the maximum of gas production occurred at about 



absorption line B and this 

 is the more marked of the 

 absorption bands of chloro- 

 phyll. 



A similar result was reached 

 by ENGELMANN and set forth 

 in a long series of papers ('81, 

 '82, '82 a , '83, '83 a , '84, '86, and 

 '87). He found that certain 

 bacteria are extremely sensi- 

 tive to oxygen, moving in the 

 direction of small increments 

 of the oxygen density. Now, 

 by putting a thread of alga in 

 the same water with bacteria 

 and subjecting the thread to 

 a "microspectrum," that part 

 in which assimilation is pro- 

 ceeding most rapidly, and in 

 which, therefore, oxygen is 

 being most rapidly excreted, 

 will be indicated by the great- 

 est aggregation of bacteria. 

 The microspectrum was pro- 

 duced by means of an appa- 

 ratus especially designed by 

 ENGELMANN for his work and 

 now manufactured by the 

 ZEISS firm in Jena. The 

 appearances seen under the 

 microscope when the spec- 

 trum falls upon the alga in 

 the bacterium - water are 

 shown in Fig. 46. The max- 

 imum aggregation (hence, 

 maximum assimilative activ- 

 ity) at the red end occurs 



FIG. 45. Curve whose ordinates are pro- 

 portional to the number of gas bubbles 

 eliminated per minute by leaves illumi- 

 nated by the various rays whose wave 

 lengths are given at the bottom of the 

 diagram, and whose number of vibra- 

 tions per second are given at the top. 

 The background of the figure is com- 

 posed of the absorption spectra of the 

 chlorophyll in living leaves. 1, 2, etc., 

 at the left, indicate the number of leaves 

 of Impatiens parviflora, which, when 

 superimposed, give the corresponding 

 spectrum at the right of these numbers. 

 The absorption at is from a fern pro- 

 thallus, that at Ale is derived from an 

 alcoholic solution of chlorophyll. I to 

 IV indicate absorption bands. Beyond 

 F there is very general absorption 

 of the highly refractive rays. (After 

 KEINKE, '84.) 



