Sinnott and Durham: Summer Squash 



179 



sistent attempts were made to obtain 

 good seed througli self fertilization. A 

 plant was watched until a male and a 

 female flower bud were found which 

 were almost ready to open. These 

 were either bagged or their corollas 

 tied up and on the succeeding morning 

 pollen was transferred from anthers 

 to stigma and the flower bagged. After 

 a few days, when the corolla had with- 

 ered or fallen, the bag was removed and 

 the young fruit tagged. As a check, 

 when the fruit was about half grown 

 an "S" with the plant's number (or in 

 crosses, the numbers of the parents) 

 was scratched with a pencil on its 

 surface and the scratch developed a 

 corky ridge which inarked the mature 

 fruit clearly. 



In the case of twenty-five of these 

 plants, self-fertilization was success- 

 fully effected and fertile seed produced. 

 In a number of others, fruits were set 

 but the seeds were weak and failed to 

 germinate. This result agrees with 

 that of other breeders who find a high 

 degree of self sterility in this species. 



In 1917 several hundred plants were 

 raised from this inbred seed. Al- 

 though in a number of cases the off- 

 spring resembled their parents rather 

 closely, in most instances a certain 

 degree of variability was still evident in 

 many plant characters, showing that 

 the parent plants had been heterozy- 

 gous. Most of the plants grown sub- 

 sequently from commercial seed have 

 also been found to be heterozygous. 



In 1917 a number of these inbred 

 types refused to set seed when selfed 

 and one or two others have been lost 

 subsequently. In every case these 

 strains were replanted in the following 

 season from reserved seed and the same 

 result obtained, showing clearly that 

 sterility or lack of vigor, and not sea- 

 sonal or other environmental differ- 

 ences were the causes of failure. The 

 other inbred lines have persisted 

 through six seasons of inbreeding and 

 show no lack of fertility. In vigor, 

 many of them are somewhat inferior 

 to heterozygous plants, but they have 

 now apparently reached a point where 

 they are maintaining themselves with- 

 out further loss of vigor or fertility. 



From year to year these inbred lines 

 have become inore constant and uni- 

 form. From five hundred to a thou- 

 sand plants have been grown each year 

 and a wide variety of types have been 

 inbred, with the result that at present 

 we have a considerable number of 

 families which are apparently almost 

 completely homozygous and may well 

 be called pure lines. New commercial 

 material has also been grown and in- 

 bred each year. 



By 1919 most of the original types 

 were breeding so true that there was 

 reason to believe that they were 

 essentially homozygous. In this sea- 

 son, therefore, crosses were made be- 

 tween various pure types involving the 

 more important character differences. 

 In 192(3 a small Fi generation was raised 

 from 20 of these crosses. In every case 

 but one, this was very uniform, thus 

 confirming the belief that both parents 

 were pure. During the past summer 

 (1921), an F2 generation of from fifty to 

 one hundred plants was grown from 

 each of these Fi types. From a study 

 of these two generations of crosses, 

 and of the segregation which took place 

 in the first few generations of inbreed- 

 ing, we are now in a position to under- 

 stand some of the facts involved in the 

 inheritance of several of the more im- 

 portant characters of the plant. 



BODY COLOR OF FRUIT 



Fruit color is perhaps the most con- 

 spicuous plant character in Cucurbita. 

 There are three main groups of fruit 

 body color; the whites (Fig. 18), the 

 yellows (Fig. 17, 30BS9-12), and the 

 greens (Fig. 19, CFl, C97, C96, and 

 24AS4). Each of these may occur 

 in different intensities, but no plant 

 has been found which could not be 

 referred definitely to one of the 

 three. During the early generations 

 of inbreeding, in the development of the 

 pure lines, yellow fruited plants and 

 green fruited plants appeared rather fre- 

 quently in lines where the parents and 

 the great bulk of the plants were white 

 fruited ; and green fruits have appeared 

 in yellow fruited lines. White fruits 

 have never arisen in yellow or green 

 lines, nor yellows in green lines. This 



