additional light. As is well known, hemp changes 

 its sex under these conditions. Our plants did 

 not escape these changes; however, the observa- 

 tions of external changes were limited chiefly 

 to the male plants, since changes in sex can be 

 observed more readily in them than in female 

 plants. Observations of the control plants re- 

 vealed that due to the influence of the shortened 

 day 34. 3% of the male plants changed sex. Irra- 

 diation intensified this process, which increased 

 as the dose was increased (as can be seen from 

 Table 22). The number of male plants which 

 changed sex under influence of irradiation in- 

 creases up to 3000 r; thereafter the process 

 becomes somewhat disorderly. It would not be 

 fair to expect uniformity, since the process is 

 also affected by the factor of differential survi- 

 val of the sexes. From this we may conclude 

 that plants which have undergone the most pro- 

 found changes, including sexual changes, are 

 the first to die. As a result of irradiation not 

 only did the number of transformed plants in- 

 crease, but the changes were more profound 

 than in the control plants. The changes pro- 

 duced by 2000 r were so great that some of the 

 male plants produced seeds which eventually 

 grew up normally (Fig. 15). One plant which at 

 first developed as a pure female plant later 

 produced a branch near the top with only male 

 flowers on it. In this way chimeric plants were 

 produced. Another plant that at first was a 

 typical female plant eventually produced male 

 flowers distributed on various levels of the 

 inflorescence. There was still another plant, 

 neither male nor female in character, which had 

 female flowers alternating with male ones. 

 There were also plants which had a male inflo- 

 rescence but only female flowers. 



These examples are completely sufficient to 

 show the wide diversity of forms that arise 

 from the simultaneous action of the shortened 

 days and X rays. These observations indicate 

 that irradiation does not induce any new changes 

 of sex, but it does intensify or accelerate these 

 processes, the action becoming more marked 

 as the dose of rays is increased. 



i| Summarizing the experiments of numerous 

 authors who have studied the effects of X rays, 

 it is possible to confirm the tremendous signif- 

 icance of X rays as a stimulator of mutations. 

 There are no characteristics that they cannot 

 change. 



The most frequent change described is that 

 of size. It is sufficient to point out that all the 

 authors note the appearance of dwarfs in the 

 descendants of irradiated plants, and, occasion- 

 ally, also of gigantic forms. Since these 

 changes concern the most diverse plants, be- 

 longing to different species, we are entitled to 

 conclude that with the help of X rays we can 

 create plants of any desired size. From woody 

 plants we require a high, even stem, since the 

 height of the plants is correlated with the length 



of the fibers. By determining the appropriate 

 dose of X rays for effect on the plants we can 

 select from among the new forms that arise 

 those which are useful, fix them by heredity and 

 obtain new material for selection of woody 

 plants. From among ornamental plants we can 

 easily obtain dwarf forms since they occur very 

 frequently. 



The general characteristics of the plants 

 change just as frequently. Many investigators 

 succeeded in obtaining by irradiation forms with 

 very little branching as well as forms which 

 branched a great deal. Plants which do not 

 branch much and which have few stems are 

 very valuable among plants which produce woody 

 fibers. On the other hand, in plants which are 

 raised for the green mass, such as fodder 

 grasses, having much branching and many 

 stems is an asset. 



The action of X rays is capable of producing 

 great changes in leaves in respect to form, 

 color, and structure. In plants where the size 

 of the leaf is of prime importance (tobacco, tea, 

 etc. ) it is possible to select from among the 

 X-ray mutants those with large leaves. The 

 wide range of leaf changes can be used for 

 decorative purposes, using as source material 

 now wide leaves, now narrow, needle -like ones 

 to create the new forms that are so prized in 

 horticulture. Changes in leaf structure can 

 serve the same purpose. It is sufficient, for 

 example, to produce a wrinkled appearance with 

 swellings in certain parts of the leaf blade. All 

 these changes can only be welcomed by horti- 

 culturalists since they increase the variety of 

 available plants. To this must be added the 

 variegated coloring of the leaves which also 

 develops quite frequently as a result of irradia- 

 tion. Leaves lose their coloring either com- 

 pletely or partially, in which case the most 

 curious distributions of white or yellow spots 

 or stripes can be observed. What unusual 

 decorative forms can be created by combining 

 changes of form and coloring of leaves! Equally 

 rich prospects open up before horticulturalists 

 in relation to changes of form and color in the 

 corolla, calyx, and fruit. 



What has been said makes clear the tremen- 

 dous significance of X rays in the creation of 

 new forms. Many of the changes which have 

 arisen in plants deserve attention not only from 

 the theoretical, but also from the practical point 

 of view. This does not mean, however, that it 

 is easy to obtain desirable changes in plants. 

 A great deal of labor is required, not only in 

 order to find doses that will change the form of 

 the plants, but particularly in order to see to it 

 that these changes are desirable ones — a diffi- 

 cult and time-consuming task. But no matter 

 what the difficulties may be, they will be repaid 

 with the success that is bound to crown the 

 efforts of the persistent investigator, sooner 

 with some plants and later with others. 



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