RAY TRACHEIDS IN ABIES 
W. P. THOMPSON 
(WITH PLATES XXIV AND XXV) 
_ A characteristic feature of the Abietineae, as opposed to the 
remaining tribes of the Coniferales, is the possession of ray tracheids 
in their wood. To this statement exception must be made, on the 
one hand for the genera Abies and Pseudolarix, from which they 
have hitherto been regarded as quite absent, and on the other hand 
for a few species of the Taxodineae and Cupressineae, in which they 
have been reported to occur sporadically. Even in the latter, 
however, they never become normal features as in the Abietineae. 
This distribution has recently received two interpretations. PEN- 
HALLOW' held that in the species where they occur sporadically 
they are appearing for the first time, and from this condition 
develop to their culmination in the Abietineae. JEFFREY,? on the 
other hand, having observed their occurrence in association with 
a wound in Cunninghamia sinensis, regards their sporadic appear- 
ance as a reminiscence of an original abundant condition such as 
exists in the Abietineae. The application of these conflicting views 
in phylogenetic considerations of the whole family is obvious. 
To the distribution briefly outlined above, the writer* recently 
recorded an exception in the case of the genus Abies. Ina wounded 
root of A. amabilis ray tracheids were discovered in considerable 
numbers. The only other record of their occurrence in the genus 
was made by PENHALLOW (loc. cit.), who observed them sporadically 
in A. balsamea. In view of the peculiar circumstances of their 
discovery and its bearing on the theories in vogue, it was considered 
advisable to investigate the material of A. amabilis fully and to 
examine other species of the genus. 
The material in which the marginal tracheids were observed 
? PENHALLOW, D. P., North American Gymnosperms. Boston. 1907. 
* JEFFREY, E. C., ea ray tracheids in Cunninghamia sinensis. Ann. Bot- 
any 22:602. pl. 37. 
’ THOMPSON, ra 2 ‘The origin of the ray tracheids in the Coniferae. Bor. Gaz. 
50: 101-116. 1910. 
331] [Botanical Gazette, vol. 53 
