59S Jeffrey . — Traumatic Ray-Tracheids in 
Abies the only well authenticated record of their occurrence is in A. balsamea 
(De Bary, Comparative Anatomy, Eng. Trans., p. 490), a record confirmed 
by Penhallow (Manual of North American Gymnosperms, pp. 88, 258, 
Boston, 1907). 
After having discussed the evolutionary history of the Abietineae 
in relation to the development of ligneous resin-canals and the presence 
of marginal ray-tracheids, a necessary preliminary on account of the clear 
and definite character of the evidence in this tribe, we are in the position to 
return to the sporadic marginal tracheids of certain Cupressineae and 
Taxodineae. Attention has already been called to the observations of 
De Bary, Penhallow, and Gothan in regard to the occurrence of marginal 
ray-tracheids in these tribes. Professor Penhallow has suggested that their 
presence in the cases described by him is the first step, so far as this 
feature is concerned, in an upward evolution, which ends in the genus Pinus . 
If we add to his observations the recorded presence of marginal tracheids 
in three Taxodineous genera, we shall have to assume, if we adopt his 
hypothesis, that this upward evolution has begun independently in six 
distinct genera. It appears extremely unlikely on general grounds that 
Sequoia , Sciadopitys, Cunninghamia , Cupressus, Juniper us, and Tlmya 
should each of them independently have varied in a direction leading 
towards the elaborate wood structure of Pinus . It seems more probable 
and more in accordance with accepted biological principles that the various 
Taxodineous and Cupressineous genera under discussion have all inherited 
their ray-tracheids as vestigal characters from a common ancestry. This 
view of the case is strengthened by a consideration of the mode of occur- 
rence of ligneous resin-canals in the genus Sequoia. It has been shown by 
the present writer (Memoirs Boston Soc. Nat., vol. v, No. 10, 1903) that in 
vS. gigantea resin-canals appear normally in the wood of the female cone and 
in the first years’ growth of vigorous vegetative branches and traumatically 
as a result of injury in the mature wood. In N. sempervirens they occur 
only as the result of wounding. It appears highly probable that S. gigantea 
is the older of the two existing species of the genus. This is rendered 
probable by the more abundant occurrence of resin-canals in this species, 
and by the fact that it shows the presence of marginal ray-tracheids which 
have not yet been found in N. sempervirens. The presence of resin-canals 
in the first annual ring and in the cone-axis of S. gigantea would on this 
interpretation constitute an example of recapitulation, while the traumatic 
resin-canals which are found in both species, as well as the marginal 
tracheids of N. gigantea , should be regarded as reversions to the ancestral 
type of wood. 
The strongest evidence, however, that neither Sequoia nor any other 
Taxodineous or Cupressineous genus has been the ancestor of the general 
Abietineous line is furnished by recent discoveries in Mesozoic Botany. 
