117 



structure. Furthermore the wood subsequently formed is at 

 first chiefly confined to two broad lobes on opposite sides of 

 the stem; while in the intermediate regions the cambium pro- 

 duces but little tissue of any kind. Later however these por- 

 tions of the cambium begin to give off a loose, soft wood 

 with broad medullary rays. This, it will be recollected, was 

 the case in /. tomentella but only to less extent with 1. ovalis. 



In 'Pliytocrene and lodes, as we have seen, the character of 

 the secondary thickening shows a close connection with the 

 leaf-arrangement, and it appears therefore remarkable that in 

 Natiatum where the leaves are not opposite as in lodes but 

 spirally arranged as in Fhytocrene the stem has never- the-less , 

 in the early stages of its thickening, a decidedly two-sided 

 structure. If the leaf-arrangement be more closely examined 

 however it is to be seen that although the leaves are spirally 

 arranged, the determining fraction of the spiral is Vi- There 

 are thus but two orthostichies , which of course lie opposite 

 each other on the axis. The bilateral symmetry of the stem 

 is therefore, in spite of the spiral arrangement of the leaves, 

 readily explained ^). In relation to the irregularities of the 

 secondary thickening the leaves stand as in Phytocrene and 

 lodes between the prominences of the wood and not in front 

 of them as in the anomalous Bignoniaceae. 



The secondary bast of Natiatum presents no features of par- 

 ticular interest. It is at first nearly confined in its production 

 to the regions opposite the prominences of the wood. Later 

 however it is altogether normal being given off from all parts 

 of the cambium. 



As the anatomy of Natiatum thus far shows much resem- 

 blance to the /(9f/^:9-species already described, it becomes a 

 matter of interest to see whether fibro- vascular formations 



1) In one instance, in a small stem from the Berlin Herbarium, three lobes 

 symmetrically arranged around the stem were observed, which would point to the 

 occasional occurrence of a V3 leaf-arrangement. And indeed this presents no im- 

 probability, considering the various leaf-arrangements and corresponding varieties 

 of structure observed in Phytocrene. Cf. Author 1. c. 



