518 BROOKLYN BOTANIC GARDEN MEMOIRS 



is obscured. As in the case of the stem colors', the different types of 

 mottling appear to involve the presence and absence of several pairs 

 of restriction factors. Only two of these patterns have been studied 

 in detail. These are the coarse- and fine-veined types. Crosses 

 between coarse and fine always give in Fi all fine, indistinguishable 

 from the "fine" pattern parent. In F2, approximately 3 fines : I 

 coarse are obtained, the actual figures being 163 fine : 49 coarse 

 (theoretical expectation 159 fine : 53 coarse). Un bagged F2 segre- 

 gates having coarse mottled seed generally breed true in F3, the few 

 cases where plants with fine mottled seeds have appeared being un- 

 doubtedly due to foreign pollen contamination. Unbagged F2 segre- 

 gates with fine mottled seeds either bred true in F3 or gave both fine 

 and coarse-mottled progeny. Coarse-mottled X the large splotched 

 type gives a dominance of the former in Fi. No F2 progeny have been 

 grown. 



Interpretation 



The inheritance of five of the sets of characters described in pre- 

 ceding pages — green and red blush stems, red blush and mahogany 

 stems, red blush and rose red stems, bloom and no-bloom, fine and 

 coarse seed pattern — so far as the Fi and F2 data are concerned, are 

 most simply interpreted as due to the presence and absence of a single 

 genetic factor in each case, making in all five genetic factors. The 

 inheritance of dehiscent and indehiscent capsules is assumed to involve 

 primarily two pairs of factors. No evidence of close linkage was found 

 between any of these seven pairs of factors, although the data were 

 taken with this end in view. 



Seed Shape and Dimension 



Castor-bean seeds differ as to shape in being oval or orbicular 

 (about as long as broad). In crosses between varieties breeding true 

 to the two types, the Fi plants are all oval seed, while in F2, orbicular 

 seeds are present in considerably over one fourth of the progeny sug- 

 gesting a 9 : 7 ratio. 



Varieties of Ricinus vary remarkably in their seed dimensions 

 and weight. Some of the commercial varieties have seeds less than a 

 centimeter long, which run about 4,550 to a pound of 450 gm., while 

 the seeds of some of the large Zanzibar ornamental types are over 2.5 

 cm. long and run only 450 to a pound. Between these are numerous 

 forms breeding true to almost every gradation in size and weight. 



A large number of crosses between these types have been made, 

 the Fi plants showing various degrees of intermediacy. All the 



