424 TUKEY 



of Agriculture, the Great Lakes lettuce from Michigan, the improved Pascal 

 types of celery from Cornell, the disease-resistant cabbage from Wisconsin, 

 the V-peaches from Canada, the Cortland apple, the Stanley plum, and the 

 Catskill strawberry from New York, the series of Haven peaches from Michi- 

 gan, the Shasta and Lassen strawberries from California, the Latham red 

 raspberry from Minnesota, the Blakemore strawberry from Louisiana — these 

 are all products of scientific plant breeding. In the United States, 55 per cent 

 of strawberry production, 75 per cent of red raspberry production, and 90 

 per cent of blueberry production are now represented by varieties created by 

 scientific effort. 



Chimaeras, polyploidy, and plant breeding. The scientist has learned 

 that many fruits are truly monstrosities, or chimaeras as they are properly 

 called. The chimaera of mythology possessed the head of a lion vomiting 

 flame, the body of a goat, and the tail of a serpent! Some bud sports, many 

 variegations, and such odd fruits as the Sweet-and-Sour variety of apple, with 

 one portion sweet and an adjacent portion sour, are now explained as chimaeral 

 and composed of a mixture of tissues of varying genetic make-up — not the 

 uniform, solid, simple creation we have often surmised. 



Basically, most plants are diploids; that is, they have two identical sets 

 of chromosomes in each cell. The raspberry, for example, has two sets of 

 seven chromosomes — a total of fourteen. Plants with more than two sets of 

 chromosomes are called polyploids. Specifically, if they have two sets, they are 

 diploids; if three sets, triploids; if four sets, tetraploids — and so on. 



Many polyploids have arisen in nature during thousands and thousands of 

 years by chance doubling of chromosomes. From these, man has selected many 

 desirable forms for cultivation, which are now the varieties of commerce. The 

 cultivated strawberry is an octoploid, with eight sets of chromosomes; and 

 the blackberry ranges from diploid to twelve-ploid. 



The thornless blackberry is found to consist of a layer of thornless tissue 

 covering an interior tissue of thorniness. When a "thornless" blackberry is 

 propagated from stem cuttings, the resulting plants are thornless because 

 the thornless tissue still continues as the other layer. But when propagation 

 is by root cuttings, the resulting plants are frequently thorny, for the reason 

 that roots arise from the internal "thorny" tissue. 



Further, a plant chimaera may consist of a mixture of diploid and poly- 

 ploid tissues, in which the typical number of chromosomes (diploid) may be 

 covered or mixed with a higher (polyploid) or lower (haploid) number of 

 chromosomes. Since polyploid tissues are frequently coarser than tissues 

 which contain a smaller number of chromosomes, the result may be apple 

 fruits with uneven pol)^loid sectors or ribs, flowers with large and small petals 

 in the same flower, and anthers which contain pollen with varying chromosome 

 number. When such anomalous flowers are used as parents in breeding, the 

 resulting progenies are in consequence confusing and unpredictable. 



