632 PROCEEDINGS OF THE AMERICAN ACADEMY. 



It cannot be too strongly emphasized in connection with the present 

 Work, that general principles in biology are either of universal validity 

 or of little scientific value, and that they cannot in certain cases be 

 admitted and in others denied. There can be little doubt moreover 

 that not a little of the existing reaction against the hypothesis of 

 evolution, is the result of a failure on the part of biologists to apply 

 evolutionary principles clearly, consistently and logically to the 

 elucidation of their investigations, even if only from the standpoint of 

 a working hypothesis. It seems clear that either there are generally 

 valid biological principles, as there are commonly accepted principles 

 in chemistry, physics and the other cognate sciences, or that biology 

 lias either not yet reached the scientific stage of development or has 

 ceased to exist on the scientific footing. There appears to be no reason 

 to adopt either of the latter alternatives. Darwin in the prolegomena 

 to his Origin of Species, emphasized the importance of the data 

 supplied by development, history, compa^ati^•e anatomy and geo- 

 graphical distribution in connection with the study of evolutionary 

 processes in living beings. Since Darwin's time experimental methods 

 have come largely into the foreground and there can be little doubt 

 that evidence derived from this source, especially when controlled 

 by an adequate knowledge of the geological history of beings now 

 living, is of paramount importance. It is proposed in the series of 

 articles of which this is the first, to discuss the origin, affinities and 

 evolution of the Araucarian Conifers, so far as appears profitable, 

 along all the important lines of investigation, indicated above. 



It will be convenient here to define the Araucarioxylon type of wood. 

 In the mature secondary wood of the trunk in the living Araucaria 

 and Agathis, we find certain peculiarities, which are taken together 

 unique among living conifers. The tracheids in these two genera 

 are characterized by the presence of pits, which are closely approxi- 

 mated and flattened, or where they occur in two or more rows, alter- 

 nating in their arrangement and polygonal in their form. The wood 

 of the Araucarian type in respect to its pitting resembles in a marked 

 degree that of the Cordaitales. The remaining tribes of existing Coni- 

 fers possess a type of tracheary pitting in which the pores are rarely 

 or never closely contiguous and when in several rows are opposite and 

 not alternating. The pits in this type too are often separated by 

 cellulose bars running transversely across the lignified walls of the 

 tracheids and imbedded in their substance. These bars of Sanio are 

 absent in the Araucarian conifers.^ They should not be confused 



1 Gerry, Eloise, The Distribution of the Bars of Sanio in the Coniferales, 

 Ann. Botany, 24, p. 231. 



