596 Jeffrey. — Traumatic Ray-Tracheids in 
section of the wound-cap. The very numerous rays are readily distin- 
guished as dark transverse stripes. It is possible to make out that none of 
those shown in the figure is provided with ray-tracheids. The amount 
of wood parenchyma is also abnormally large in the region of the wound- 
cap. Sections from the opposite side of the stem are characterized by 
a more normal amount of wood parenchyma and a normal number of 
medullary rays. The latter in some instances, as has been described above, 
show the presence of ray-tracheids. A careful examination of this and other 
fragments of wood has failed to reveal the presence of ray-tracheids, except 
in the region representing the annual rings formed after injury and in the 
part of the circumference of the wood more remote from the actual wound. 
It appears from the account given in the paragraphs above that in the 
genus Cunninghamia there are found, in definite relation to injury, marginal 
tracheids in the rays such as are typical of the Abietineae. It would 
perhaps be possible to regard these as a mere abnormality did they not 
also occur in other representatives of the Cupressineae and Taxodineae. 
Their presence is apparently significant. In the Abietineous genera, Pinus , 
Picea , Pseudotsuga , and Larix , not only are marginal tracheids a charac- 
teristic feature of the rays of the normal wood, but ligneous resin-canals 
likewise occur normally. In the Abietineous genera, Cedrus , Tsuga , Adzes, 
and Pseudolarix , ray-tracheids are normally present in only the two first 
named genera. Resin-canals are. entirely absent in all four in the mature 
wood, except as the constant accompaniment of injury. In the first years 
growth of the root, and in a few cases in the cone axis and in the first 
year s growth of vegetative branches , resin-canals occur normally in the four 
last-mentioned Abietineous genera. It is a reasonable conclusion on 
ordinary biological principles to consider, on the basis of the evidence of 
the living Abietineae alone, that the presence of ligneous resin-canals is 
ancestral for that tribe, and that the normal occurrence of resin-canals 
in the first annual ring only, as a result of injury to the mature 
wood, in the genera, Cedrus, Tsuga, Abies, and Pseudolarix, represents 
phenomena of recapitulation and reversion respectively. This view is 
much strengthened by the consideration of the fossil forms. It has been 
recently shown by the present writer that there are the best of reasons from 
the anatomical palaeobotanical side for regarding Pinus as the oldest 
of the living Abietineae, and as related to the archaic genus Prepinus 
(Jeffrey, E. C., Structure of the Leaf in Cretaceous Pines, Ann. Bot, 
vol. xxii, pp. 207-20, 1908). Prepinus, in the anatomical structure of its 
leaf, a feature recognized on all hands to be most important and significant, 
shows a remarkable detailed resemblance to certain Cordaitales. In this 
genus the structure of the wood, so far as the presence of resin-canals is 
concerned, was identical in structure with living and Cretaceous Pines. 
Further, Fliche has obtained structural evidence for the existence of Cedrus 
