200 
cases where a decided angle occurs, the pore is considered bor- 
dered (Jehéft). Sanio, in his work on the wood elements (Holz- _ 
kérper), probably took another standard, as he has in several 
cases described pores as bordered, which, by this test, must be 
considered simple; for example—/raxinus, Betula and others. 
The principal genera of sixty-seven families were examined. 
Of this number there are only eight families in which the libri- 
form tissue contains both bordered and simple pores, eighteen 
contain only bordered, and thirty-four only simple pores. The re- 
maining seven families contain genera which do not agree in this 
respect. These present various points of interest in regard to 
the parallelism between anatomical and morphological character- 
istics, therefore they will be referred to more fully in the second 
part of the work. 
If we begin with the most complex type, or that containing 
the greatest variety of elements, we find this illustrated by the 
eight families containing both kinds of pores in the libriform. 
Here we find not only the highest degree of differentiation of 
tissue, but also the greatest variety of means for water transport, 
according to the assumption that the greater amount of water is 
carried through the cell lumen. One example taken from this 
class will illustrate this and also the manner of arrangement of 
the tissues, in which is found a supposed adaptation to this func- 
tion of the bordered pore. We omit here the part supposed to be 
played by the cells of the medullary ray and wood parenchyma, 
in the upward transport of water—not because it is less import- 
ant, but on account of its lack of connection with the present 
subject; then we have, as before stated, the tracheze, which take 
the first rank as water carriers, both on account of their size 
(diameter) and their open communication with each other; then 
the thin-walled tracheids, next the thick-walled or libriform 
cells with bordered pores, next the real libriform cells, or those 
containing only simple pores. The woody tissue of Quercus 
furnishes a typical illustration containing all these elements with 
great variation in size. If we make a cross-section extending 
through the growth of a single year—that is, giving us the pic- 
ture of the so-called annual ring—we find the elements arranged 
in the following order : 
