174 BOTANICAL GAZETTE [august 



Owing to the cellulose nature of these bars, they have dropped out 

 in the course of fossilization, and now are represented by white 

 lines. Their occurrence near the pith of this specimen, which is 

 clearly transitional between the Araucarineae and Abietineae, is 

 quite in keeping with their occurrence in the cone axis of the living 

 genus Araucaria, and in the first annual ring of the fossil Araiicari- 

 oxylon described earlier in this paper. In all these cases the bars 

 of Sanio are to be interpreted as vestiges of w T hat was characteristic 

 of the mature wood of their ancestors, retained only in certain con- 

 servative regions of these reduced forms. Viewed in this light, it 

 seems evident that their presence in the first formed wood of an 

 araucarian Cupressinoxylon is another indication of the derivation 

 of the Araucarineae from the Abietineae. 



stem is representative of a considerable number 

 m each other onlv in slight and unimportant details 



The 



three diagnostic features are (i) wood parenchyma scattered 

 throughout the year's growth, (2) thin-walled ray cells, and (3) scat- 

 tered pits on the radial walls of the tracheids, without bars of Sanio 

 intervening. All these are shown in figs. 27 and 29. In such 

 structures as arrangement and size of medullary sclerites, there 

 is considerable divergence. For example, in the specimen repre- 

 sented in figs. 25 and 26, the individual stone cells are grouped in 



small 



form 



There is not a little variation also in the pitting of the radial walls 

 of the rays, though in all the horizontal and end walls are unpitted. 

 Usually there are one to four small piceform pits to each cross- 

 field, but in fig. 31 is shown a specimen with a single large pit. 

 That each large pit originates from the fusion of two small pits is 

 indicated by the occurrence of two partially fused pits, end to end. 

 Similar stages in pit fusion were described in the case of one of the 

 Pityoxyla from the same deposit. Another interesting feature of 

 this specimen, shown in fig. 32, is the resinous exudation from the 

 rays into the tracheids. Similar appearances are common in the 

 living Agathis, and thus serve to establish another bond between 

 these transitional Mesozoic forms and living members of the 

 Araucarineae. 



