Intranucleolar bodies in maize pachytene microsporocytes

study may be summed up as follows: After treatment with alkali-urea, three size orders of chromatin fibrils can be recognized in salivary gland chromosomes: (1) 20 &thick fibrils, and sometimes thinner ones, which are usually found in well-stretched axial fibrils and sometimes in loop fibrils, though mostly in the background. They supposedly represent bare DNA. (2) 30 A fibrils, which exist both in the axis and loops. They supposedly represent DNA-histone fibrils. (3) 100 &thick fibrils, which exist mostly in unstretched parts of loops, and evidently represent secondarily-coiled DNA-histone fibrils of the second order. The fibrils which are somewhat thinner (about 70 8, or even less) can be observed sometimes in divided segments and in wellstretched regions of 100 8, fibrils. In thin sections of untreated salivary gland chromosomes, both the band regions and the unstretched interbands consists of about 100 A fibrils (actually 50150 A thick). In bands, however, fibril coiling is clearer and fragments of higher orders of coiling can be observed (cf. also SORSA and SORSA 1967, 1968 a, b).