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Silver does not stain all cytological structures with the same intensity. The chemical basis for differential silver staining is unclear, but differences in protein side groups available to react with silver are likely involved. These include amine, carboxyl, phosphate, sulfhydryl and hydroxyl moieties. Here we report an investigation of the chemical groups that could be involved in salt-nylon silver staining of onion root tip squashes. Based on the results, we conclude that SN silver staining primarily depends on the presence of tyrosine hydroxyl groups, and we propose a mechanism for staining.

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KHUTHIER AND ROBERT~ON a t 24' with 1-iodobutane, only 15.7% (glc) of the new amine was obtained. Small impurities of N-(n-butyl)-N-methylaniline ( 6 ) , N-(n-pentyl)-N-methylaniline (7), and p-(n-butyl)-N-(n-butyl)- N-methylaniline (11) were detected in the reaction mixture by glc: ir 3.44 s, 3.52 s, 3.60 m, 6.20 s, 6.61 s, 6.80 m, 7.45 m, 8.18 w, 8.41 w, 8.62 m, 8.85 w, 9.45 w, 10.57 w, and 12.42 + m; pmr 6 0.92 (3 H), 1.61 (4 H), 2.48 (2 H), 2.80 (6 H), and 6.78(4 H, A&, 9).Attempted Lateral Alkylation of 3.-(1) I n two parallel experiments, 3 was prepared. I n one the reaction mixture from the exchange and hydrolysis was analyzed (4,53%; 7,6.2%; 8, 12%); the other was treated with 25 mmol 2 and 51.5 mmol 1-iodobutane a t -15" and the mixture stirred during 4 hr, allowing it to warm up to 15". Glc analysis gave 4 (37.0%), 7 (6.0570), and 8 (11.0%). No lateral alkylation of 3 was achieved by the standard alkyllithium-alkyl iodide technique. (2) To 3 from 5 mmol of 1 and 22.5 mmol of 2 (24 hr, 25") was added 5 ml of anhydrous ether and, a t O", 12.5 mmol of 1-iodobutane. The temperature was allowed to go up to 20" during 3 hr. The quenched reaction mixture was analyzed (glc): 3 (40%), 7(4.50j0), and 8 (4.4'%). No lateral alkylation was therefore achieved by the addition of 1-iodobutane.Lateral Alkylation of p-Bromo-N,N-dimethylaniline (1). Lithium-Bromine Exchange of p-Bromo-N-(n-pentyl)-N-methylaniline (14) with n-Butyllithium (12).-p-Bromo-N,N-dimethylaniline (1) (5 mmol) and n-butyllithium (2) (20 mmol) were mixed at -10" and, as soon as a homogeneous solution formed, 1-iodobutane (10 mmol) was added. After stirring for 1 hr a t -8', the solution was gradually warmed up to 18' in 23 hr.The quenched reaction mixture contained (glc) 4 (23%), 7(2.55%), 8 (1.2y0)! 1 (14.90/0) and 14 (6%). The dry hexane mixture was then stirred 24 hr with excess n-butyllithium a t room temperature and quenched as usual. Both brominated amines disappeared completely while the 7 to 8 ratio increased from 2.13 to 3.1. p-Deuterio-N,N-dimethylanilhe @).-This compound couldbe easily obtained by adding deuterium oxide to the exchange mixture and distilling the product:M ir 3.27 m, 3.33 m, 3.50 s, (21) R. Willstaetter and R. Pummerer, Chem. Ber., 87, 3733 (1904).The Schmidt reaction of 2,4,6-cyclooctatrien-l-one in concentrated sulfuric acid produced 8,g-dihydrophthalimidine (4), which could have formed only from the migration of the methylene group. The other isomeric product, 3a,ga-dihydroindolone, which would have required the migration of the vinyl group, was not observed. On the other hand, the same reaction in trifluoroacetic acid produced 5H-tetrasolo [ 1,5-a] azonine (5) and its valence isomer 5a,9a-dihydro-5H-tetrazolo[5,l-a]isoindole ( 6 ) as the main products, with a small amount of 4.The Schmidt reaction of 2,4,6-cyclooctatrien-l-one (1) is expected to produce 2,9-dihydro-2-oxoazonine (2) and 2,3-dihydro-2-oxoazonine (3) from the migration of J (1) (a) This is publioation number 23-69 from Colorado State University. (b) T.