REPORT OF THE SECRETARY 



71 



coarse-structured biological plates which are prepared by forming 

 a surface inoculation of algae upon agar. A special plate holder 

 has been constructed which can be thoroughl}^ sterilized in an auto- 

 clave, and which completely surrounds the algal plate even during 

 exjjosure, thus insuring freedom from contamination. A thermo- 

 couple is driven across the spectrum and automatically records the 



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Figure 4.- 



2800 



I 



SIOO 



-MerciU'y arc spectrograms : A, direct thermocouple record ; B, microphotometer 

 record of photograph ; C, microphotometer record of algal plate 



intensities of the lines under the same conditions as those to which 

 the algae have been exposed. The algal plates are then photographed 

 and a densitometer record made just as one would with an ordinary 

 photographic spectrum. 



Figure 4 shows, first, the direct thermocouple record obtained au- 

 tomatically, curve A ; second, the microphotometric record of a photo- 

 graphic spectrogram of the same general region, curve B ; and third, 

 such a microphotometric record of the algal plate, curve C. 



