150 JOHN H. SCHAFFNER Vol. XXII, No. 6 



plete separation, both because of their position in the ground, 

 close together and with the buds pointing in the same direction, 

 and because of the remarkable similarity of the vegetative 

 characters and similarity in size. Occasionally there is a dif- 

 ference in size of the individuals, or in the length of the sterile 

 tips of the spadices, or in the time of emergence from the 

 ground. There is no reason why such differences should not be 

 decided, since the original fission of the bud may be quite 

 unequal. In the dichotomous branches of Vernonia baldwinii 

 Torr. and V. altissima Nutt,, for example, there is frequently a 

 decided difference in the length and complexity of the two forks.* 

 There might also be a difference in the more specific vegetative 

 characters occasionally, for the same reason that the two sides 

 of a symmetrically bilateral body may differ in the characters 

 expressed as, for example, the differences in the details of vena- 

 tion of pairs of insect wings, differences in the lobings of the 

 two halves of a leaf, differences in the colored spots of the heads 

 of certain turtles which are usually symmetrical, and differences 

 in the color of the eyes of dogs and men, where one occasionally 

 finds individuals with one eye blue and the other brown. The 

 same differences of expression must take place occasionally 

 after separation of two bilateral halves of an egg or vegetative 

 bud and it is, therefore, possible that identical twins may differ 

 decidedly in very important characters. 



Not only are the Arisfema twins, so far discovered, all 

 remarkably alike in vegetative characters but they are of the 

 same sex. Some are staminate pairs, some are carpellate, and 

 some intermediate with both staminate and carpellate flowers 

 on the spadix, just as is the case with normal individuals. But 

 the most remarkable characteristic exhibited by the bisporan- 

 giate twins is that so far they have been identical or nearly 

 identical in the distribution, position, and numbers of the 

 staminate and carpellate flowers. Since the elaboration of the 

 hypothesis of the Mendelian nature of sex, it has been supposed 

 by some that the fact that identical or duplicate twins are 

 apparently always of the same sex gave a very strong pre- 

 sumption in favor of the correctness of the chromosome-linked 

 or Mendelian hypothesis. This is, however, not at all the case 

 as will appear from the evidence given below, derived from a 



* ScHAFFNER, JoHN H. Unusual Dichotomous Branching in Vernonia. Ohio 

 Jour. Sci. 19:487-490. 1919, 



