GENETIC AND CYTOLOGICAL EFFECTS 265 



deficiencies and 8 without. In addition there was one "dehciency trans- 

 location, . . . three-armed, the plant being deficient for parts of chromo- 

 somes 1 and 10." De Boer (unpublished) found several similar cases of 

 deficiency and deficiency translocation. 



Although all the deficiencies appeared to be terminal, the distinction 

 between terminal and nonterminal deficiencies is not convincing in maize 

 without critical cytological material. Nonhomologous pairing may give 

 a known interstitial deficiency the appearance of a terminal deficiency. 

 De Boer (19-15) has presented evidence of ultraviolet-induced terminal 

 deficiency free from this difficulty. The gene bz is a plant color gene 

 located on the short arm of chromosome 9, and stocks of maize are avail- 

 able bearing a terminal knob on this arm. Ultraviolet- and X-ray- 

 induced deficiencies of Bz, in a stock with the terminal knob, were exam- 

 ined cytologically, the criterion of terminal deficiency being loss of the 

 terminal segment including the knob. Nonhomologous pairing of an 

 interstitial deficiency could result in a terminal unpaired region of the 

 untreated chromosome, but would be recognizable by the presence of the 

 knob, or a portion of the knob, on the deficient chromosome. Among six 

 Bz deficiencies in the ultraviolet series, four showed terminal deficiency of 

 the short arm of chromosome 9. The other two were deficiency translo- 

 cations. Among nine Bz deficiencies in the X-ray series, none was a 

 terminal deficiency. These alterations included one interstitial defi- 

 ciency, three ring-9 configurations, and five deficiency translocations. 



Straub (1941), in a study of somatic metaphase chromosomes, has 

 shown that ultraviolet-induced translocations occur with appreciable fre- 

 quency in Gasteria. From some 1800 embryos obtained from the fertili- 

 zation of untreated eggs by exposed sperm, 210 were selected for cytologi- 

 cal study because their weak development suggested that they might 

 possess chromosomal abnormalities. Of these, 75 showed chromosomal 

 changes as contrasted to 1 from 300 control embryos. Four of the 

 embryos were chimeras showing some cells with normal and some with 

 altered chromosomes. Straub considered these to be similar to the frac- 

 tional endosperm deficiencies induced by ultraviolet in maize. In the 

 remaining 71 embryos, 72 apparently terminal deficiencies were detected 

 in the long arms of the four G chromosomes, which could be recognized 

 by their conspicuous satellites. The breaks giving rise to these deficien- 

 cies were largely concentrated in the neighborhood of the centromere. Of 

 the remaining cytological abnormalities, five were translocations, includ- 

 ing one of an undefined but probably reciprocal type, two which were 

 defined as "isochromosomes," one dicentric chromosome, and one ring 

 chromosome. 



Barton (1954) has compared the chromosomal effects of X-ray and 

 ultraviolet treatments in the tomato {Ly coper sicum esculentum Mill.). 

 In this plant each of the 12 chromosomes at pachytene shows a densely 



