The excitation functions of the elastic scattering 12C(p, p)12C and the reactions 12C(p, p′)12C (4.44 MeV) and 12C(p, α)9Bg.s. have been measured at θ = 175° in the region of the first T = 32 state in 13N with high energy resolution. A straightforward resonance analysis of the elastic scattering data yields Γ = 1.10 ± 0.09 keV, Γp = 210 ± 11 eV and ΓpΓ = 0.191 ± 0.017. The results are compared with shell-model predictions. The additionally measured angular distributions of the elastic scattering 12C(p, p)12C above and below the resonance are compared with optical model calculations. The combination of the present results for Γp and Γp/Γ with previous results for Γγ/Γp and ΓγΓp/Γ yields Γγ = 27.0 ± 2.2 eV as a new determination of the 13N(T = 32, 15.07 MeV → T = 12, 0 MeV) γ-decay width. The comparison with the analogous γ-decay in 13C is discussed with respect to the charge symmetry of corresponding ΔT = 1 γ-transitions in mirror nuclei.

The lay-out and the ion-optical structure of the beam handling system at the Bonn Isochronous Cyclotron is described. The following beam preparation modes are possible with two double monochromator systems: (1) double dispersive with an extremely high momentum resolution of 30 000; (2) double dispersive with an adjustable dispersion matching with a magnetic spectrograph; (3) nondispersive, nearly isochronous, variable momentum resolution up to 8000, adjustable time of flight resolution below 0.5 ns; (4) achromatic with a transmission of 100%. The practical experiences in operating the system and achieving the design performances are discussed. The results of rigorous test measurements are given.

I t has been widely accepted that oxidation is a major cause of the degeneration of the exine layer of spore and pollen grain walls. Recently this factor has come into consideration regarding the fine structure of these walls (Afzelius, 1956). Afzelius demonstrated that oxidation may change a "granular laminated structure into an amorphous granular" one, the latter showing no additional effects of oxidation. When Saintpaulia ionantha pollen is fixed for 24 hours with 1 per cent osmium tetroxide (pH 7.5) or with 10 per cent formaldehyde (for less than 12 hours; pH 8.0) followed by OsO4 for 3 or 24 hours, the exine fine structure is uniformly granular (Fig. 1). Avoiding the oxidative catalyst (benzoyl peroxide) by substituting ultraviolet light for hardening the methacrylate has no effect on the exine. I t must be remembered, however, that OsO4 is itself a powerful oxidizing agent. When the time of formaldehyde fixation is increased to 24 hours and is followed by OsO4 for 3 hours, a slightly amorphic appearance of the exine results (Fig. 2). When pollen is subjected to 24 hours of leaching in water between the 24 hour formaldehyde fixation and 3 hour OsO4 fixation periods, the exine degeneration is severe (Fig. 3). No degeneration occurs if OsO4 fixation is used first or if leaching of unfixed pollen is followed by OsO4 fixation. Also, no degeneration occurs if the pollen is treated with saturated ammonium oxalate for 23 hours prior to formaldehyde fixation. I t appears that a reducing agent such as formaldehyde can chemically alter the exine and cause its degeneration. This serves to question the advisability of storing pollen in preservatives containing formaldehyde until such time as experiments testing the effects of various dilution levels of formaldehyde and time of exposure to them are made. Since even the ultrastructure of

Double fixation followed by standard electron microscopical techniques yielded good results in the preparation of S. ionantha meiocytes, microspores and pollen grains for the present investigation. Delimitation of microspores occurs by cleavage furrowing which apparently involves the enlargement of vacuoles between the developing microspores. Columellae are the first exine structures formed in the mesocolpium regions of the microspores, and mesine is found about the same time. The tectum and endexine are formed next but the germinal furrows remain without wall elaboration until later. These stages occur within the PMC wall. Thus, the basic architecture of the S. ionantha pollen grain wall is established early in microspore development. The intine is formed later. The structure and development of the germinal furrow differs somewhat from that of the mesocolpium. At maturity, the furrow consists of a thick, laminated mesine which is flecked with exine and underlain by a thick intine. This structure is modified in the germ pore area. The intine first appears in the germinal furrow regions, becomes thickest there, and is the last wall layer to be completed. Appearance of the perine coincides with the final stages of wall development. The wall structure of aborted pollen is similar to that of other pollen except that no intine is found. Duplication of genes by polyploidy does not alter the development and structure of S. ionantha pollen grain walls. Variation in the number of germinal furrows and increased wall thickness were the only observed effects of polyploidy.