530 Heritable Spiral Torsion. 



race of Dipsacus sylvestris torsns, during over thirteen 

 years, together with a long series of further observations 

 on the inheritance of this anomaly in other plants, have 

 proved that this character is as heritable as other anomalies 

 are. Plate VI gives a view of a culture of this race, re- 

 produced from a photograph of one of my beds. 



Real spiral torsion only occurs in those species which 

 normally have a decussate or whorled disposition of the 

 leaves. It consists in the substitution of a spiral arrange- 

 ment for this. The leaves arise from an unbroken spiral, 

 along which they are attached to one another more or 

 less closely to their bases (Fig. 123). This close spiral 

 is sometimes interrupted and normal internodes are inter- 

 calated in the twisted part. Not infrequently the torsion 

 is limited to a greater or a lesser part of the stem (com- 

 pare, e. g., below^ Dianthiis, Fig. 129). Indeed no sin- 

 gle stem is completely abnormal from the very beginning. 



As might be expected the fusion of the base of tlie 

 peduncles into a continuous band results in an inhibition 

 of the longitudinal growth of the stem. The internodes 

 cannot elongate normally, and as they strive to extend, 

 they partly unwind the leaf spirals. In consequence the 

 spiral becomes steeper and not infrequently unwinds so 

 much in the up])er parts of the stem, i. e., those parts 

 which normally grow in length, as to become a straight 

 line. When this occurs the leaves and their axillary buds 

 arise in a longitudinal series on one side of the stem 

 (Fig. 122). Obviously this can only be reached by the 

 stem twisting itself in the opposite direction to that of 

 the leaf-spiral (Fig. 123). Inside the twisted stem, 

 if it is hollow, the diaphragms which normally occur at 

 the nodes, do not exist as such, but are united together 



