IgIo] THOMPSON—RAY TRACHEIDS III 
whose end is bent along a ray for a remarkable distance. Such 
tracheids are very common in the 
cone axis, more than half the rays 
showing at least one in some part of 
their short course. Evidently they do 
the work of the ray tracheid, and 
probably represent the first step in a 
process of turning and _ shortening 
which, as described above, ends in 
the production of ray tracheids. 
Similar bent ends are sometimes to 
be found in the young stem, and are 
evidently to be interpreted in the same way. 
Fic. 14.—P. Sirobus: cone axis: the 
end of a tracheid bent along a ray. 
Relation to albuminous cells 
In the light of what has been said of the origin of ray tracheids, 
an interesting circumstance is furnished by their relationship to the 
albuminous cells of the ray. STRASBURGER (7) points out the 
homology between the latter and sieve tubes. “The albuminous 
cells are higher than the ordinary cells of the ray and like sieve tubes 
have sieve areas, soon lose their contents, and ultimately collapse.” 
They are then virtually ray sieve tubes. Now in the Abietineae, 
Where ray tracheids are numerous, albuminous cells were always 
found conterminous with them through the cambial region. This is 
illustrated in fig. 15 even for a row of interspersed ones. In the Arau- 
carineae and Taxaceae, where there are no ray tracheids, there are no 
albuminous cells. In those Taxodineae and Cupressineae where no 
Tay tracheids were seen, no albuminous cells were found. And in 
Thuja, where ray tracheids occur sporadically, the only albuminous 
cells were those lining up with ray tracheids. Albuminous cells are 
then always associated with ray tracheids (an interesting exception 
is noted below). This association and their sieve tube character 
indicate that they bear the same relationship to ray tracheids as the 
Sieve tubes to wood tracheids. They thus afford valuable collateral 
evidence of the tracheary origin of their representatives in the wood. 
The exception referred to is found in Abies balsamea. Here almost 
“very ray passing through the bast has albuminous cells on its margin, 
