Abstract. Pyrogenic plants dominate many fire-prone ecosystems. Their prevalence suggests some advantage to their enhanced flammability, but researchers have had difficulty tying pyrogenicity to individual-level advantages. Based on our review, we propose that enhanced flammability in fire-prone ecosystems should protect the belowground organs and nearby propagules of certain individual plants during fires. We base this hypothesis on five points: (1) organs and propagules by which many fire-adapted plants survive fires are vulnerable to elevated soil temperatures during fires; (2) the degree to which burning plant fuels heat the soil depends mainly on residence times of fires and on fuel location relative to the soil; (3) fires and fire effects are locally heterogeneous, meaning that individual plants can affect local soil heating via their fuels; (4) how a plant burns can thus affect its fitness; and (5) in many cases, natural selection in fire-prone habitats should therefore favor plants that burn rapidly and retain fuels off the ground. We predict an advantage of enhanced flammability for plants whose fuels influence local fire characteristics and whose regenerative tissues or propagules are affected by local variation in fires. Our ''pyrogenicity as protection'' hypothesis has the potential to apply to a range of life histories. We discuss implications for ecological and evolutionary theory and suggest considerations for testing the hypothesis.

No abstract

Fourteen pyrazolones were synthesized from the corresponding mono or disubstituted cyanoacethydrazides or cyanoacetphenylhydrazides and evidence concerning their constitution was obtained from chemical reactions and ultraviolet absorption spectra determinations. A mixture of two tautomeric forms was obtained when 4-benzyl-3-amino-5-pyrazolone was prepared; it was converted to a single form by treatment with hydrochloric acid. The following compounds, as far as the authors are aware, have been prepared for the first time: 4-methyl-3-amino-5-pyrazolone, 4-methyl-2-phenyl-3-amino-5-pyrazolone, 4-ethyl-3-amino-5-pyrazolone, 4-ethyl-2-phenyl-3-amino-5-pyrazolone, 4-(2-phenoxyethyl)-3-amino-5-pyrazolone, 4-(2-phenoxyethyl)-2-phenyl-3-amino-5-pyrazolone, 4-(3-phenoxypropyl)-3-amino-5-pyrazolone, 4-(3-phenoxypropyl)-2-phenyl-3-amino-5-pyrazolone, 4-phenyl-3-amino-5-pyrazolone, 4-benzyl-3-amino-5-pyrazolone, 4-benzyl-2-phenyl-3-amino-5-pyrazolone, 4,4-dibenzyl-3-amino-5-pyrazolone, 4, 4-dibenzyl-2-phenyl-3-imino-5-pyrazolone, 4,4-(2,2-spiro-indanyl)-3-amino-5-pyrazolone.

The method of deter~uining sulphate acid ester in unstabilized cellulose nitrates by hydrolysis in acetone/water solution was evaluated. The precision of duplicate determinations for cotton and wood cellulose nitrates containing about 100% sulphate ester was -0.1 to +5.9% and +0.4 to +9.2%, respectively. With cellulose nitrates containing 69-43% and 69-47% sulphate ester, i t was +1.8 to +13.4% and +0.4 t o +21.0%. The sulphate acid ester content of both unstabilized cotton and wood cellulose nitrates increased with decreasing nitrogen content.

Cotton linters and wood cellulose were nitrated in parallel experiments with a series of mixed acids and the prodl~cts examined for nitrogen and sulphate content. A higher degree of nitration was obtained with the cotton cellulose, and the sulphate content of the nitrated cotton increased steadily with increasing corlcentratio~l of sulphuric acid in the nitration medium while the sulphate content of the wood cellulose passed through a maximum value which depended on the degree of nitration. The sulphate content of the cotton cellulose nitrates was higher than that of the ~vood cellulose nitrates when the nitrations were performed under similar conditions. IKTRODUCTIONThe sulphate content of crude, but well washed, cellulose nitrate prepared from mixed acid varies from about 0.2 to 3.0y0, expressed as sulphuric acid, according to the compositioll of the nitric-sulphuric acid mixture. The total sulphate and the proportion of sulphate ester tend to increase with decreasing nitrogen content (2, 4).The object of the present work was to compare the degree of nitration of cotton linters and wood cellulose obtained when the composition of the mixed acid used was the same, and to establish the relation between the sulphate conteilt of iinstabilized cellulose nitrate and the sulphuric acid content of the mixed acid. Cellz~lose NitrateCotton linters and wood cellulose were nitrated with mixed acids, using the method given in a previous publication (2). The mixed acids were analyzed by standard methods. The total sulphate content in the cellulose nitrates was determined as barillin sulphate (3). The nitrogen content was obtained by the Devarda method. RESULTS AND DISCUSSION Degree of Nitratio~zMany nitrations of cotton linters and wood cellulose were carried out using a variety of mixed acids, in order to determine the relation between mixed acid constitution and nitrogen content. 1~1iles (4) states that "the degree of nitration possible in any mixed acid is chiefly a function of acid coinposition". I11 the present work, the results obtained were in accord with this statement. The range of mixed acids varied from 65.0 to '73.670 for the sulphuric acid, froin 9.0 to 25.5% for the nitric acid, and from 8.4 to 20.4% for the water. The compositioi~ of the mixed acids and the correspondi~lg nitrogen contents for the cotton cellulose nitrates together with a few results reported by X4iles and Milbourn for ramie fiber cellulose nitrates are given in Table I.Miles and 111ilbot1rn (5) nitrated ranlie fiber with a wide range of mixed acids, and expressed their results for the relation between "composition and degree of nitration" in the form of a triangular chart. The results obtained for the nitration of cotton linters