233 
The Pores of the Libriform Tissue.* 
By EmILy L. GREGORY, Ph. D. 
The results of the investigations in this direction served, in 
most instances, to confirm this supposition. Some care was 
taken to discriminate between small trachez and tracheids by 
use of macerated preparations. These attempts were not wholly 
satisfactory, owing to the impossibility of examining every sepa- 
rate cell. They served, however, to prove that in some instances 
the cells referred to by anatomists as tracheids, are really small 
trachee. For example, in Rodznia, a large number of tracheid- 
like cells were found to communicate directly with each other by 
means of a circular opening in the partition wall. These two 
classes, small trachez and tracheids, seem to pass into each other 
here, by gradual transition stages, some being found to possess 
an opening at one end, thus communicating directly with the 
next cell, while at the other end no trace of an opening could be 
found. 
Enough examples were studied to show that great variety 
exists in the number of elements of different woods. In 
Quercus, as before described, all the elements occur, so also 
in Ligustrum. Others were found to lack one or more, as 
Ribes, which lacks the thin-walled tracheids; Comarum, the 
simple-pored libriform ; Berderts, the bordered-pored libriform, 
and also the wood parenchyma. Quite a large number have 
only large and small tracheze; such are Populus, Salix,. Acer, 
Fraxinus and others. Here occurs the difficulty before men- 
tioned, of deciding accurately between tracheids and small 
trachee. In many woods where openings were found between 
the cells it was only by the most careful manipulation, and it is _ 
impossible to say with certainty that they fail entirely in any of 
the above mentioned cases. On the other hand, when they are 
found to exist in any part of the specimen under consideration, 
we can only infer that they exist throughout in the same element. 
Only two examples were found which contained only large 
trachee and simple-pored libriform. These are Betula alba and 
Corylus Avellana. Here the trachee appear to be of a nearly 
