The Autoploids 329 



ing 1.7 inni. in thickness as compared with about 2.7 mm. for the 4X 

 seeds. This feature is of practical vahie in sorting 3X and 4X seeds 

 if the tetraploids are left to open pollination from tetraploid and 

 diploid pollen in the same field. In Figure 1.S.2 the sizes of diploid 

 and tetraploid seeds are contrasted. 



If longitudinal sections are made of mature seed, the diploid, or 

 2X, seeds show a completely filled cavity, while the 3X and 4X seeds 

 fill the space up to 82.5 and 90.1 per cent, respectively. Accordingly, 

 a weaker germination is a characteristic of the ?>X seeds. This becomes 

 a point of considerable practical importance and must be overcome 

 ^\ith j)roj)er cidturing conditions. Such seed cannot be j)lanted in 

 the field with dijiloid and be expected to produce the same field 

 stand for both varieties. 



Genetic markers are helpful to distinguish triploid fruits from 

 tetra])loid and diploid. Dark -green, parallel striping is dominant over 

 smooth color, therefore fruits pollinated by diploid with the stripe 

 character show in the triploid if tetraploid fruits are non-striped. 

 Tetraploid fruits may have this mark (Fig. 13.2) . 



Yielding capacity of triploid plants exceeds the diploid by almost 

 twice. Variations a])pear de])ending upon the particidar varietal 

 combinations. Ihe increase in number of fruits per unit area is 

 particularly significant both as to number and weight. 



Triploid fruits are seedless because chromosome distribution to 

 gametes is irregular. Trivalent associations form among the 33 

 chromosomes. At reduction division, less than 1 per cent of the 

 gametes obtain a complete set of 1 1 chromosomes necessary for a bal- 

 anced gamete. Ninety-nine plus per cent have numbers ranging from 

 1 1 to 22 chromosomes. Sterility is induced, and pollination with 

 viable pollen does not produce seed because of female sterilitx. \\4ien 

 pollinations are prevented on triploids, fruits do not set. 



Special cultivation procedures are necessary for triploid A\ater- 

 melons: soil shoidd be sterilized, seed planted in beds kept at 30°C., 

 and transplantation procedines carried oiu to insme a field stand of 

 vigorous plants. Once the triploid is established, its growth exceeds 

 that of the diploid and continues longer during the season. A ratio 

 of 4 or 5 triploid plants to 1 dijjloid provides adequate pollen to set 

 fruit on triploids: the latter become parthenocarpic. 



A sLuiimari/ing j:)aper by Professor H. Kihara of the Kyoto Uni- 

 versity, Kyoto, japan, on triploid watermelons. ]niblished in the Pro- 

 ceedings of the American Society lor Horticultural Science,-'" was 

 recognized as an outstanding contribution to horticidiinal science. 

 Accordingly, this jniblication was chosen to receive the Leonard H. 

 \^aughn Award in \'egetable croj)s. The published works from \'ol- 

 iinies 57 and 58 of the Proceedings were considered in the competition 

 for this honor. 



