LEPIDODENDRON 163 



pith was replaced by scattered parenchyma. Although 

 limited to the place of bifurcation, this condition is 

 of some interest, because analogous anomalies occur 

 among the higher plants at the present day. The 

 cambium, in fact, shows similar eccentricities in its 

 behaviour wherever it occurs, quite irrespective of 

 taxonomic relationship. As we trace the two branches 

 higher up, we find that the stele in each gradually 

 regains its normal circular form. (Fig. 66, from a 

 forking branch of L. selaginoides, shows the steles in an 

 intermediate state.) 



Unequal dichotomy simply means that one branch 

 of the fork is much smaller than, and sometimes differ- 

 ently organised from, the other. This no doubt often 

 occurred in the vegetative region, in cases where a main 

 axis bore a comparatively small twig, as an apparently 

 lateral branch. Unequal dichotomy was, however, of 

 common occurrence in connection with the fructification, 

 when one branch of a dichotomy was fertile, while the 

 other remained vegetative. Such cases, however, will 

 be considered in the next chapter. 



Anatomically, unequal dichotomy is characterised 

 by the behaviour of the stele. It is frequently the case 

 that the smaller of the two branches has no medulla. 

 Then, instead of the two equal horse-shoes described 

 above, we find only a small part of the main stele 

 diverging to the minor branch. Sometimes a segment of 

 the wood was cut out, as it were, from the stele, leaving 

 a small opening, which soon closed up. The segment 

 destined for the branch was thus solid from the first 

 {e.g. Lepidophloios fuliginosus, Fig. 69, b'). In other 

 cases the strand of wood passing out to the smaller 



