homozygous family continued to multiply by means 

 of self-pollination. Stubbe used a voltage of 5 to 

 10 kilovolts, 5 to 10 milliamperes, the distance 

 from the anticathode was varied from 10 to 20 

 centimeters, and the exposures were varied from 

 5 minutes to 5 hours and 20 minutes. However, 

 an even greater number of experiments were 

 carried out with a voltage of 20 to 70 kilovolts. 

 Flower buds at various stages of development 

 were subjected to radiation. This was quite pos- 

 sible to do with a single inflorescence, in view 

 of the cluster -like shape of the inflorescence of 

 Antirrhinum ma jus . The immediate consequence 

 of X radiation was that all the buds undergoing 

 reduction-division experienced a serious delay 

 in development. This delay can be so marked 

 that further development becomes impossible. 

 Other buds develop into flowers, but they be- 

 come infertile, although the growing point con- 

 tinues to develop. Sometimes he observed zones 

 of growth depression, which affected up to 10 

 buds. After that normal flowers appeared again. 



In 1928, 77 plants were irradiated, and in 

 1929, 4507 [45079] 2 Xj offspring were selected; 

 of these 397 had clear indications of transforma - 

 tion [which arose from 67 parent plants (1930a)]. 

 Stubbe found 30 dwarfs, 209 narrow -leafed 

 plants, 5 which resembled the radiomorphs de- 

 scribed by Stein in 1937*, 11 with variegated 

 leaves, 9 with blue-green leaves, 4 with mutated 

 flowers, and 126 stunted plants. 



In a second series of experiments performed 

 in 1929*, seeds from a single pod in each of the 

 mutated plants (all of them were self-pollinated) 

 were planted. Stubbe' s [1930a] description of 

 morphological changes indicates that the action 

 of X rays induces the appearance of an unusual 

 variety of forms. At first Stubbe called them 

 mutations only conditionally, but further experi- 

 ments showed that the major part of these 

 changes had a hereditary character. Stubbe 

 divided these changes of form into five groups: 



1) Dwarfs. Among them the most extreme 

 deviations from the norm are represented by 

 plants whose growing points are absent. With 

 age the storing up of nutritive substances in the 

 leaves, causes a puffing up of the epidermis in 

 the region of the growing point from which, 

 eventually, new shoots issue bearing narrow 

 leaves. The viability of these dwarfs is negli- 

 gible. Other plants - semi -dwarfs - reached 

 a height of 14 centimeters. One of them had 

 two flowers which were infertile (in the male 

 parts), the tubules of the corolla were split as 

 far as the calyx. A third type of dwarf plants 

 dispalyed negligible growth with a strong incli- 

 nation toward branching and plagiotropic direc- 

 tion of growth. The leaves of all the dwarf 

 plants were very narrow, small, and often had 



2 Ed. note: Text in error; correction is as indicated. 



needlelike points on their ends. 



2) Narrow -Leafed Forms . The width and 

 length of leaves, type of branching, form of 

 flowers, and the fertility of these flowers vary 

 within very wide limits. The narrow -leafed 

 forms are usually accompanied by splitting and 

 other deformations of the flowers. The most 

 extreme change accompanying the narrow -leafed 

 type is represented by a single plant whose 

 petals had a tendency to turn green, the anthers 

 were absent and, apparently, formed part of the 

 gynecium, the style was funnel-shaped, the 

 upper and lower labia were shortened. Nearly 

 all of the narrow -leafed forms had impaired 

 fertility. In the majority of the plants the an- 

 thers were quite brown and empty, or filled 

 with white, empty pollen. 



3) Plants Resembling Radiomorphs . These 

 were described by Stein* as resulting from the 

 exposure of snapdragons to radium. This type 

 of mutant can be recognized very early since 

 even in young plants dark streaks appear on the 

 blades and the leaves become wrinkled, which 

 intensifies during the growth of the leaves and 

 determines their deformation. In especially 

 strongly altered shoots the wrinkling of the 

 leaves carries over into the flowers, which 

 causes the upper and lower lips to crack and 

 round out. However, the fertility of these plants 

 is completely normal. Some shoots at first dis- 

 play these changes, after which the development 

 assumes its normal course. When flowers of 

 this changed branch [strain] are self-pollinated, 

 individuals appear among the descendants with 

 distorted flowers having irregular numerical 

 relationships [of parts]. 



4) Plants with Variegated Leaves of the 

 Albomaculata Type . The hereditary character - 

 istics are transmitted only by the maternal line. 

 One X-ray mutant (basiflora) is of particular 

 interest. Its shoots are at first green; then, 

 after several weeks, they become variegated. 

 The young leaf blades are green only at their 

 tips, whereas the central part of the leaf is 

 white and begins to turn green (starting at the 

 central vein) only with age. Old leaves have 

 the normal green coloring. 



5) Stunted Plants . While remaining pheno- 

 typically normal, these plants lag behind their 

 age group in development and have extremely 

 reduced viability. 



In further experiments Stubbe (1930b) worked 

 out the methodology of the experiments more 

 thoroughly. Seeds and seedlings were subjected 

 to X rays. The seeds had been previously 

 soaked for 2 to 3 days in water. The seedlings 

 were irradiated when they were 3 to 4 weeks 

 old, at a time when the cotyledons had attained 

 their full development and the first leaflets 

 were beginning to appear. Only 20 to 50% of the 

 seeds came up, but after the first few days of 



44 



