The Autoploids 323 



met. Since there are diploids as well as naturaltetraploids within the 

 group, some .hybridization Avould appear possible. The crossing of 

 autotetraploids with natural tetraploids offers a method to be tried. i^* 



Plihinu pratcii.sc was made uj) in chrdmosomal series, ranging Irom 

 di])loid to twelve-jjloid.^i'^ Analyses ior vigor, lorage production, and 

 quality were clone to check the optimum number, below or above 

 which poorer performance was noticed. Progenies with 5() to 64 

 chromosomes were more vigorous than the 42-chromosomal plants or 

 the polyploids with 84 chromosomes. This principle of optimum 

 numiicrs must be recognized in polyploidy breeding. Hexaploid 

 Phleuin nodosum was made by first doubling the chromosomes with 

 diploid P. nodosutn.^-'- The tetraploid was treated again and a hexa- 

 ploid was isolated. Of special interest is the close correspondence 

 between the natural species, P. pratense L., and the hexaploid, P. 

 nodosum. 



Lolium perenne in the tctrapU^d state was compared to the dip- 

 loids.i'^"' Morphological and physiological studies brought to atten- 

 tion characteis such as winter injury, sugar content, dry matter, mois- 

 ture, leaf structure, tillering, and flowers. The autotetraploids of 

 seven species of grasses were compared in regard to both morjiho- 

 logical and cytological details. No specific advantages were demon- 

 strated for the tetraploids. 



Autotetraploid Sudan grass, Soio^lnim vulgare var. sudunense. and 

 Johnson grass, .S'. halopense, were hybridized to make a j^asture 

 species.-'' Autotetraploid Sudan grass incorporated better forage 

 characters into the hybrid. One observation confirmed that the auto- 

 tetra])loid would hybridize while the diploid Sudan grass always 

 failed. Later generations followed for this hybrid segregated for the 

 dry and juicy stalk quality. The segregations were closer to 35:1 than 

 20.8:1, meaning that random chromosome segregation had occurred. ^'^ 

 These polyploids showed a tremendous possibility for selection. 



/^./• — 9; Polyploidy in fruit, xn'getable, jloivcr. and forest species. 

 Polyploidy and fruit improvement in the United States have been 

 summarized in this way. The problem is like that of a "i)uilcler sur- 

 veying the possibilities of his materials and the usefidness of his tools." 

 Materials are enormous and tools are now available. Ciolchicine is 

 one of those im])ortant tools, while the materials include an abun- 

 dance of i^lants in nature and under cultivatic^n. "4 he onl) limits are 

 his blueprint, his time, and his industry. "•^•' 



The diploid, woodland strawbcrrx. Fragtiriu I'csca. 2}i = If, is 

 found in many parts of the northern hemisphere. Cultivated varieties 

 are octojiloids, 8^; =: 56. Autotetra])loicls from F. vesca, 4n ^= 28, ^vere 

 made and crossed with 56-chromosome cultivated strains. Such hy- 

 brids were 42-chromosome hexajiloids. These were crossed back to 



