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In the first few experiments Af was passed through Dowex-2-chloride twice and absorbed twice with 50 - 100 mg sweet clover tissue powder.

The intermediate sera were also similarly absorbed with tissue powder.

Sections of sweet clover stem and root tumors were treated with 1: 10 solution of Af for 30 minutes, washed in buffered saline for 15 minutes, stained with Af for 30 minutes, and washed for 15 minutes in Aj.

Such sections showed bright yellow-green specific fluorescence in the cells of the pseudophloem tissue ( Lee and Black, 1955 ).

This specific fluorescence was readily distinguished from the light green nonspecific fluorescence in consecutive sections stained with 1: 10 dilution of NS and Af or with Af alone.

Unstained sections mounted in buffered glycerine or sections treated only with NS or Af did not show such green fluorescence.

Sections of crown gall tissue similarly stained with either Af and Af or NS and Af also showed only the light green nonspecific fluorescence.

However, the nonspecific staining by the Af in tumor sections was considered bright enough to be confused with the staining of small amounts of WTV antigen.