516 BROOKLYN BOTANIC GARDEN MEMOIRS 



cross of bloom X no-bloom, the Fi plants had bloom, but were only 

 lightly covered as compared with their "bloom" parent. In F2, the 

 plants approximated a ratio of 3 bloom: i no-bloom as usual, though 

 many of those with bloom were lightly covered as in Fi. 



Dehiscent and Indehiscent Seed Pods 



The seed pods or seed capsules of Ricinus, in most varieties, are 

 dehiscent, the seeds being thrown out of the mature ripe capsule 

 with great force. These are known as "poppers" in regions where 

 the plant is cultivated commercially. A few varieties have inde- 

 hiscent capsules, the seed being retained within the pod for several 

 months. This characteristic considerably reduces the cost of harvest- 

 ing the beans, as only two or three collections a season are necessary, 

 whereas "popper" varieties must be harvested twice a week or more, 

 to prevent loss. The castor-bean plant matures its seed over a very 

 long season. The "non-popping" variety with which the writer 

 experimented has thin-walled, comparatively brittle capsules, while 

 all the popping varieties have capsules with thick, leathery walls. 

 The dehiscent characteristic is probably due to cells similar to those 

 found in the fern sporangium, which rapidly lose their moisture content 

 when the capsule matures and contract, thus breaking apart the cap- 

 sule and expelling the seed. 



Crosses of "popper" with the "non-popper" variety gave all 

 "poppers" in Fi and approximately 9 "popper": 7 "non-popper" in 

 F2 (the actual figures being 343 pop.: 259 n.-pop., the theoretically 

 expected being 338.4 pop.: 263 n.-pop.). 



In F3, seed from unguarded F2 "popper" segregates gave either all 

 "poppers," or "poppers" and "non-poppers." 



Seed from unbagged "non-popper" F2 segregates produced in most 

 cases only "non-poppers." The "popper" and "non-popper" vari- 

 eties involved in the crosses were very distinct, but the F2 populations 

 were somewhat difficult to classify, as many of the "non-poppers" 

 would, under very favorable conditions, slightly pop. These were 

 usually thin-walled, brittle capsules, showing, perhaps, that the nature 

 of the capsular tissue (thick, leathery or thin and brittle) modified the 

 "popping" or "non-popping" characteristics. On the assumption 

 that two pairs of characters are concerned in this cross, each of which 

 is primarily determined by the presence and absence of a single factor, 

 the results may be interpreted by regarding the "popper" character 

 as due to the presence of both the factor for popping (A), and the 

 factor for thick, leathery capsules (B). In the presence of A and the 

 absence of B, the capsules would have thin, brittle tissues, but pop 

 slightly, although not sufficiently to class them as "poppers." In the 



