i 
234 
uniform size, no small ones being present. In these two in- 
stances it must be inferred that either the simple-pored libriform 
cells do contribute in no small degree to the passage of water, 
or that the local needs are satisfied by some arrangement of the 
numerous large trachea. Although we have, at the beginning, 
excluded the consideration of the cells of the medullary rays and 
wood parenchyma, as not materially affecting the question of the 
nature of the libriform tissue, the suggestion may be allowed here, 
that a factor of such importance in the water transport, as this 
probably is, may come in play in a somewhat different manner 
here than in cases where the number of elements is greater. 
The simplest woody tissue was found in Veronica Andersoni ; 
a woody stem of two years’ growth was found to contain only 
large and small trachee and simple-pored libriform, and no 
medullary rays nor wood parenchyma. In one year growths of 
Chelone and Digitalis the same structure was found, but the 
woody growth was not so well developed. The small trachee 
here might easily be mistaken for tracheids, and it is not possible 
to say with absolute certainty that all of these are really trachez. 
The greater number examined were found to communicate di- 
rectly, therefore the others, having the same appearance in other 
respects, are supposed to agree also in this one. 
In the literature on this subject, examples are given of one 
year’s stems of certain Cruciferee which contain no medullary 
rays, but these cases of Veronica, Chelone and Digitalis appear 
to be the first ones found where wood parenchyma also fails. It 
is the more remarkable as in other genera of the same family 
well developed and complex forms occur. 
It is conceded at the outset that there is ground in the fore- 
going pages for the following objection, namely: That the 
hypothesis of a functional difference between bordered and sim- 
ple pores is here based mainly upon another supposition, that of 
the water transport through the cell-lumen, which is itself only a 
supposition, and has yet to be substantiated by proof. 
This objection, however, cannot be urged against the consid- 
eration of the question simply from the anatomical-systematical 
standpoint. It must be conceded, that without regarding this 
supposed function of the pores, a certain interest attaches itself 
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