1006 BIOLOGICAL EFFECTS OF RADIATION 



Nubbin, the formula of which is 2n — 1-2 + 1-9 + 2-5, parts of the 

 1-9 and 2-5 chromosomes compensate to make the equivalent of the 

 missing 1-2 chromosome, leaving the -9 and the -5 portions as extra 

 chromosomal material responsible for the peculiarities of the type. 

 Compensating types have been reported for 8 of the 12 chromosomes of 

 Datura. 



Three pure-breeding types, synthesized with chromosomes which had 

 been modified by radiation, have been reported in Datura. Their 

 formulae are as follows: 



1. 2n - (11-12)2 + (2-lM2)2 



2. 2n - (1-2)2 + (-1)2 + (2-2)2 



3. 2n - (13-14)2 - (23-24)2 + (2-14)2 + (13-23)2 + (-24)2 



All three types are similar in appearance since they have excess -2 

 material; they breed true since the excess material is attached to an 

 essential chromosome. 



Stadler (71) described experiments showing that mutations may be 

 induced in barley by radium rays, as well as by X-rays, which he had 

 previously demonstrated. The source of the rays was 50 mg. of radium 

 sulfate sealed in a thin glass tube within a tube of silver 1 mm. thick. 

 Barley seeds, germinating in stacked watch glasses, were exposed con- 

 tinuously for 12 to 24 hr., at distances ranging from 1.5 to 11 cm. "The 

 maximum dose (applied to seeds immediately above and below that 

 containing the radium tube) was well below the limit of tolerance." 

 Out of a total of 1039 exposed seeds, 3 "mutants" were reported; out of a 

 total of 1341 control seedlings (unexposed), no mutants. 



The following year, Goodspeed (28) showed that abnormalities of 

 cytological behavior, external morphology, and fertility may be induced 

 in various species of Nicotiana by exposure to radium rays as w'ell as 

 X-rays. "Heritable, qualitative alterations" of various kinds followed 

 treatment of the sex cells of A''. Tabacum. Lethality was conspicuous, 

 and both dominant and recessive changes in vegetative and floral char- 

 acters were found. The paper deals chiefly with the effects of X-ray 

 treatment. 



Later, Goodspeed (29) reported the occurrence in Nicotiana progenies 

 from X-rays and radium treatments of three instances of apparent gene 

 alteration, which he called "recessive monogenic mutations," namely, 

 pink flower color, pistillody of the androecium, and albino seedlings. 



In 1930 Constatin (20) presented a summary of studies of the genetical 

 effects of radium rays and X-rays, also an extended bibliography. 



Brittingham (12) studied the effect of rays from radon (emanation) 

 on germ cells of Oenothera Lamarckiana and Oe. franciscana. An unfil- 

 tered tube of radon was inserted in a flower cluster parallel with the flower 

 buds, thus exposing all the buds of the cluster at distances varying from 

 direct contact to 4 cm. As the flowers opened after treatment they were 



