241 
Myrtus forms an exception to all the other genera by the absence 
of, at least, any visible simple-pored libriform. In Eucalyptus 
globulus a few cells only were found to contain simple pores. In 
Eucalyptus perfoliatus the number of cells containing simple pores 
is much greater; in a number of other genera, Lepfospermum, 
Melaleuca, Metrosideros, Eugenia, etc.,the quantity of each element 
is about the same. 
From this ‘somewhat cursory survey of the various families 
and groups, the conclusion reached is, that there is a certain 
parallelism between this peculiar anatomical structure and the 
morphological-systematical characteristics which decide the 
limits of the family, the principal cases which furnish exceptions 
to this statement being themselves genera of doubtful character. 
Outside the limits of the family, however, this parallelism 
does not exist. That is to say, while the families of two or three 
groups were found to correspond in this respect, the greater num- 
ber of groups showed no such correspondence in the structure of 
the libriform tissue. 
A few words of explanation are necessary in regard to the 
terminology used in speaking of the various elements of the woody 
tissue. No particular system has been followed, not from any lack 
of systems, but rather from the opposite reason. Nearly every 
writer on this subject suggests a special method of classification. 
Of all the different articles on woody tissue that of Sanio is per- 
haps the most thorough and exhaustive. His method of classi- 
fication is extremely difficult to use, as will be seen by the follow- 
ing explanation. He divides the wood elements, whose long axes 
are parallel with the long axis of the stem, into three classes: paren- 
chymatic, tracheal and libriform elements. He distinguishes the 
tracheids from the bordered-pored libriform cells by the difference 
in the size of the border, and further, he says the real libriform cells 
never have spiral thickenings, which are almost always present in 
the tracheids. As they are not always present, and as he gives no 
concrete example which may be taken as a measure for the size of 
the border when we wish to decide whether a cell is to be classed 
with the tracheal or libriform element, we have no means to 
determine definitely. 
A more recent article has appeared, “ Vergleichende anatom- 
