106 



Applied Biophysics 



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FIG. 8. Photomicrographs of chromosomes at metaphasc blocked by colchicine in 

 pollen tubes of Tradcscautia. («) Chromosome-break (i) witli sister chromatid- 

 unions in both the centric and acentric fragments, (b) Chromatid-breaks, C 



FIG. 9. Photomicrograph of part of the nucleus of a salivary-gland cell of 

 Drosophila, showing an inversion-loop (lower left). The loop is pro.luced by tb.e 

 intimate pairing of the parts of the inversion-chromosome with the homologous parts 

 of the normal chromosome. 



lost as differentiation proceeds ; in certain circumstances radia- 

 tion may promote the process of differentiation. Apart from a 

 direct lethal effect, cells may be so injured by radiation as to be 

 incapable of successful division, and thus either perish on at- 

 tempting mitosis or }:)roduce n(jnvial)]e daughter cells. The 

 degeneration which is linked with interference with mitosis can 

 be distinguished from that resulting from the breakdown of the 

 so-called resting cells. ^-' 



