26 Mutual Independence of Hereditary Characters 



species will change from its normal type into another form 

 of whorl, and in numerous plants with decussate leaves, 

 single branches with three- and more-ranked whorls 

 have been observed. The Fuchsias and the Weigelias of 

 our gardens, are common examples. The transitions from 

 one number in the whorls to the other usually take place 

 by leaps, in such a way that the whole shoot springing 

 from one bud is alike in this respect; however, branches 

 with another number in their whorls will frequently de- 

 velop from its terminal bud or its lateral buds. More 

 rarely a shoot will change, during its development, from 

 one number to another, as is the rule, for example, in 

 Lysimachia vulgaris. Intermediate forms between two- 

 or three- and four-ranked whorls are exceedingly rare, 

 although from our present knowledge, they may develop 

 quite readily, and have actually been observed from time 

 to time in most plants with whorled leaves. 12 I mean those 

 whorls in which one leaf is more or less deeply split at its 

 apex, while the mid-vein forks. This splitting occurs in 

 all conceivable degrees and leads to a complete doubling 

 in those leaves which bear two blades on one cleft petiole. 

 Consideration of numerous examples gives the impression 

 that the single whorl-forms are antagonistic to each other, 

 and that each tries to exclude the other. It is rare that 

 they do not succeed in this effort, and then we get the 

 above mentioned leaves with the forked mid-vein, the 

 complete series of transition of which, from one leaf to 

 two leaves has been figured and described by Delpino. 13 



Therefore, even such qualities, which in the devel- 

 oped plant exclude each other, are miscible, apparently 



12 Cf. Delpino, F. Teoria generale della Fillotassi. Atti R. 

 Univ. Genova 4: 197. 1883. 



Loc. cit. p. 206, Taf. LX, Fig. 60. 



