7l6 THE AMERICAX XATL'RALIST. [Vol. XXXVIII. 



In preparing this table, the various anatomical features have 

 been chosen with reference to ( i) the constancy of their occur- 

 rence, (2) their structural prominence and ( 3 ) their obvious 

 relation to diagnostic purposes. In their horizontal extension, 

 an attempt has been made to arrange them in accordance with 

 the law of frequency, as well as with reference to their relation 

 to development, in such wise that while the spiral tracheid is 

 assumed to be the most primitive type of the vascular structure, 

 the presence of two kinds of cells in the medullary ray may be 

 held to express the highest form of development. To the mem- 

 bers of the series so constituted we may then assign arbitrary 

 \ alues in arithmetical sequence from one to seventeen ; while those 

 subordinate characters which are represented by different forms 

 of distribution may be regarded as forming a second series simi- 

 larly valued. Any primitive or other character which has 

 become obliterated through development may be held to retain 

 its original value with respect to the general course of such 

 development, and it is always indicated by — . Vestigial struc- 

 tures occurring sporadically are designated by (i), and to them 

 one half the value of the fully developed character is assigned. 

 All normal features are designated by x ^ which becomes x -f 

 when they show development toward the next higher form, or 

 by X _ when they show a definite tendency to degeneration. 

 Sporadic characters which are obviously in the line of develop- 

 ment are indicated by (o), but they are assigned only half values. 

 On this basis it is possible to arrange a sequence of genera and 

 species in such a manner as to exhibit a progressive develop- 

 ment from the simple Agathis with a minimum of characteristics 

 to the complex Pinus in which the greatest number of anatomi- 

 cal features are involved. Furthermore, through such a series 

 It is i)(^ssible to determine the relative position of the various 

 genera by percentage values, and this gives the most valuable 

 msight into the approximate relations of the various members 

 within the general line of descent. Such relations are deter- 

 mined not only tor each anatomical character, but for the collec- 

 tive characters. Reducing these facts to a graphic form, the 

 accompansing curves will assist in making the relations more 

 clear, especially in emphasizing the general course of develop- 



