22 



EDWARD C. JEFFREY ON 



entirely absent in the woody tissues of the stein. The only exception to this rule is 

 their occasional occurrence in the wood of the reproductive axis (species of Abies) and 

 in the first annual ring of vigorous branches in mature trees (species of Abies) . Resin 

 ducts occur normally and without exception in this group in the center of the primary 

 wood of the root. Resin canals are also present in the cortex but in the genera Tsuga 

 and Pseudolarix the cortical canals are confined to the reproductive organs and to the 

 leaves. In the Abieteae the integument of the ovule is relatively thick, and the cone 

 scales are usually deciduous. 



As a further preliminary to the discussion of the phylogeny of the Abietineae 

 attention must be called to certain principles or canons of comparative anatomy, derived 

 from the study of living and fossil plants, which are of such recent origin that they 

 have scarcely as yet been definitely formulated. One of the most important of these 

 canons is, that ancestral structures are apt to linger on in the reproductive axes after 

 they have disappeared from the vegetative organs. Solms-Laubach ('90) first called 

 attention to this principle in the matter of the arrangement of the bundles in the 

 cones of the Cycads, which is much simpler in the reproductive axis than in the vege- 

 tative stem, and according to his view is archaic. The most important contribution 

 to this generalization, however, has been made by Scott ('97) . He pointed out that 

 in certain Cycads there are present, in the axis of the cone, mesarch bundles compar- 

 able to those found in the vegetative axes of certain of the fossil and ancestral 

 Cycadofilices. He draws the inference that the mesarch type of bundle is primitive 

 for the Cycads and has lingered on in certain instances as an anatomical feature of 

 the male and female cones. The present writer ('99) has directed attention to the fact 

 that the course of the fibrovascular bundles in the cones of the more modern Cala- 

 mi tes is the same as that found in both vegetative and reproductive axes of the more 

 ancient Calamites included in the genus Archaeocalamites ; for in the latter there is 

 no alternation of the course of the bundles at the nodes, a feature retained in the 

 cones of the later Calamites and to some extent even in the modern Equisetum. " In 

 the younger stages of the development of the fibrovascular bundles of the cone in 

 Equisetum there is present a cambium, another point of resemblance to the Cala- 

 mites, ancient and less ancient, which were characterized by the presence of very 

 marked secondary woody growth. In this connection it may be pointed out that 

 Cushman (:03) has noted the resemblance of the leaves occurring on the reproductive 

 axis of certain higher plants to those first appearing in the seedlings. Jackson ('99) 

 had previously shown that the nepionic or earlier leaves of phaenogamous seedlings 

 in many cases present remarkable resemblance to the leaves of allied fossil species. 

 These illustrations will serve to indicate that there is a strong tendency towards the 

 retention of ancestral characteristics in the reproductive axes of vascular plants. 



