514 BROOKLYN BOTANIC GARDEN MEMOIRS 



of seed. Because of this, the Fi generation plants, in some cases, were 

 grown in isolated cultures, instead of being bagged. In this way 

 large quantities of seed were obtained for growing F2 populations. 

 In most cases, enough seed from bagged Fi plants was obtained to 

 check up the F2 results from the unbagged seed. A large number of 

 F3 families were grown from seed of unbagged F2 plants. The per- 

 centage of cross-fertilization among the F2 individuals appeared to 

 be small. 



Experimental Work 

 Stem Color 



Stem color in castor beans can be roughly classified into five cate- 

 gories (see Plates XXIII and XXIV) — bright green, green with reddish 

 blush on sunny side, carmine or rose red, mahogany red, and purple 

 (dark red). The development of each type of red coloration depends, 

 to some extent, on sunlight, particularly the red blush class. In 

 shade, plants of this class have green stems. 



These red color types are similar chemically, so far as solubility 

 tests with their pigments are concerned, since all the red pigments are 

 soluble in water containing a trace of chloroform, but remain insoluble 

 in alcohol, xylol, or in pure chloroform. The red pigment is a sap 

 color, occurring in the epidermal palisade cells in the leaf and stem 

 (see Plate XXIII), also in parenchymatous areas of the stem, especially 

 in the pith in some varieties. The different shades are apparently 

 due (as observed microscopically) to different concentrations of the 

 pigment in the cells and to a difference in the amount of pigmented 

 cell area. From evidence thus far obtained, the writer is inclined to 

 regard the hereditary differences between the red types as due to the 

 presence and absence of several color dilution factors, each of which 

 modifies the expression of a red pigment producing factor common to 

 all, except, of course, the green-stemmed class. Still further modi- 

 fications in coloration appear to be due to the presence and absence 

 of a pattern restriction factor, in the absence of which the stems and 

 leaves are mahogany red, or purplish red if "bloom" is present. 



In crosses, red blush X other red blush varieties always gave 

 only red blush Fi and F2 offspring. Red blush varieties X green- 

 stemmed varieties and the reciprocal always gave all red blush in Fi 

 and approximately 3 red blush : i green in F2. 



Actually obtained 113 red blush: 43 green 



Theoretically expected 117 " " 39 " 



In F3, seed from unbagged F2 green-stemmed plants generally gave 

 all green plants, while unguarded seed from F2 red blush plants either 

 gave all red blush or both red blush and green-stem families. 



