544 PROCEEDINGS OF THE AMERICAN ACADEMY. 



remarkable way the validity of the doctrine of recapitulation, in 

 accordance with which the young individuals of living species may 

 pass through in their earlier stages of development the condition 

 found typically in their extinct ancestors of more or less remote 

 geological time. 



The first annual ring of the living species of Agathis and Araucaria, 

 unlike the Araucarian woods of the Araucarioxylon type, from the 

 American Cretaceous, shows only slightly and often sporadically the 

 departure from Araucarian pitting characteristic of Brach^^oxylon, etc. 

 Not more than two or three tracheids next the protoxylem in the most 

 favorable cases illustrate this feature. In this respect the existing 

 woods of the Araucarian type show themselves, as might be ex- 

 pected, less retentive of ancestral characters than is the case with the 

 similar woods from the Cretaceous. In the case of the normal type 

 of Araucarian wood, not only the approximation but also the alterna- 

 tion of the radial pits of the tracheids are characteristic features. 

 Figure e, Plate 5, shows under a comparatively low magnification, 

 the structure of the tracheids adjoining the protoxylem in the cone of 

 Araucaria BidwiUii. It is easy to make out that the pits in the tra- 

 cheary elements of the secondary wood nearest the scalariforni ele- 

 ments of the protoxylem, are arranged for the most part in opposite 

 pairs. Moreover even with the low magnification employed it is 

 clear that the pits in question are not flattened by mutual, approxi- 

 mation. In other words we have the conditions present, so far as the 

 radial pitting is concerned, which are typical of the wood of the Abie- 

 tineae and other tribes of Conifers. Farther awa}^ from the protoxy- 

 lem the pitting passes into the typical araucarian condition. Figure/, 

 Plate 5, shows a part of the last more highly magnified. On one side 

 the tracheids still retain some indications of the spiral and reticulate 

 sculpture of the protoxylem. On the other tracheids of the secondary 

 wood have made their appearance. They are characterized, however, 

 by a distinctly non-Araucarian arrangement of the pits and by other 

 remarkable and important features. The pits are separated from each 

 other by appreciable intervals. The most remarkable feature, how- 

 ever, shown by the tracheids in* this region is the presence of dark 

 discontinuous stripes crossing the tracheids transversely between the 

 pits. These dark stripes in the photograph often fork at the ends 

 and represent cellulose bands in the substance of the tracheid walls. 

 They are in fact typical bars of Sanio (not to be confused with the 

 'Balken' or trabeculae of Sanio, which are a very different thing), 

 found normally in all the tribes of Conifers except the Araucariineae. 



