1913] HOLDEN—RAY TRACHEIDS 63 
the original Pityoxylon line has persisted to the present day as the 
_ Abietineae. In some of them ray tracheids have become more 
and more elaborated (hard pines); in others they have become 
reduced until they occur only traumautically (A b7es) or are entirely 
lacking (Pseudolarix). In the Taxodineae and Cupressineae they 
have become more and more reduced until they are present normally 
in only a very few species, and traumatically in certain others. 
Since the taxads, podocarps, and araucarians never have ray 
tracheids, it is evident that if they came off from the Abietineae, 
it must have been at some time before the Middle Cretaceous, 
probably in the early Mesozoic. 
To this suggested Upper Cretaceous origin of the Taxodineae 
and Cupressineae, it might be objected that in the Lower Cretaceous 
and Jurassic there are present Cupressinoxyla, together with leafy 
twigs, cone scales, cones, etc., which have been referred to Sequoia 
and allied forms. There is however nothing to prove that these 
woods belong to the Taxodineae or Cupressineae rather than to the 
a podocarps or taxads, which, as pointed out above, probably origi- 
nated very early in the Mesozoic. As to the twigs, cones, etc., 
have been shown to be araucarians and not Sequoia at all (15 
and 16). 
Summary 
1. Ray tracheids are present normally in Pityoxyla from the 
Middle Cretaceous on, and in the Abietineae. 
| 2. Ray tracheids are present traumatically in the Taxodineae 
and the Cupressineae. 
3. On the evidence of traumatic recapitulation of ancestral 
characteristics, it is evident that the Taxodineae and Cupressineae 
are descended from the Abietineae, having sprung from that line 
at some time after the Middle Cretaceous. 
4. Since ray tracheids are universally absent in the Podocar- 
_ pineae, Taxineae, and Araucarineae, these lines must have come off 
_ from the Abietineae at some time before the Middle Cretaceous. 
5. These conclusions are corroborated by a study of geological 
records and of other anatomical Strae wares, as resin canals, wood 
parenchyma, etc. 
