THE CANONS OF COMPARATIVE ANATOMY 239 



of the cones frequently manifested the presence of vestiges of 

 centripetal wood, although xylem belonging to this category has 

 wholly disappeared in the vegetative axis. The value of this 

 generalization can scarcely be overestimated. During the interval 

 of nearly twenty years dating from Scott's brilliant discovery, 

 much additional evidence has been supplied in support of the 

 conservatism of the anatomical structure of the reproductive axes. 

 For example, it has been shown by comparison of the vegetative 

 organization of Mesozoic conifers with the anatomical structures 

 found in the ovuliferous cones of living forms that the latter fre- 

 quently perpetuate features which have vanished in the vegetative 

 parts. This is manifestly the case in the abietineous and arauca- 

 rian conifers which compete with each other for the claim of being 

 the most ancient representative of the coniferous stock. The cone 

 in both Pinus and Agathis presents numerous Mesozoic features 

 which have disappeared elsewhere in the stem organs of existing 

 species belonging to these genera. 



The value of the anatomy of reproductive axes cannot be 

 estimated so highly in the case of the angiosperms, since the 

 relatively slight development of fibrovascular structures in flowers 

 and inflorescences leaves less scope for the appearance of phylo- 

 genetically significant structures. This situation needs to be 

 particularly emphasized in view of some recent highly fallacious 

 attempts to utilize the anatomy of reproductive axes in working 

 out evolutionary sequences in the woody dicotyledons. Clearly in 

 this instance only structures are significant which find adequate 

 development in the somewhat slender annual woody cylinder of the 

 flowering parts of perennial dicotyledons. In the monocotyledons 

 the restrictions on interpretation are still greater on account of the 

 usual absence of secondary growth in this great division of the 

 angiosperms. In the application of the doctrine of conservative 

 parts to the reproductive axes of the angiosperms it must be 

 recognized that a little knowledge is a dangerous thing. 



It has been made clear in the preceding paragraphs that the 

 doctrine of conservative parts is well exemplified by the leaf and 

 is manifested in the stem by the more archaic axes connected with 

 reproduction. The situation in the organs cited has for a long time 



