240 
eo course, entirely impracticable. There is possi- 
bly a suggestion of such transition in the genus 
Liriodendron, B, before referred to, where the 
borders in the same cell were found to vary a 
little in form, some having the typical lenticular 
form, others inclining more to a circular shape. 
This, however, can be considered only as a sug- 
gestion. ; 
It is, however, quite diffierent when the ques- 
tion of size alone is considered. Several fami- 
lies were found in whose different genera all 
variations in the size of the border oceur. For example, the 
~ family Ericacee, of which the genus Erica offers, perhaps, 
the best example found of this supposed beginning stage 
of the border. Here the form corresponds exactly with those 
found in the other genera, and we can trace the increase in size 
from one genus to another till we reach the genera Vaccinium 
and Oxycoccus, where the border attains a medium size. 
In other families there was found great variation in the num- 
ber as well as size of the pores. In the genus Drimys of the 
family Magnoliacez, the number of pores is about as great as the 
surface of the cell wall will allow, and the border quite as large 
as in some of the conifers. In ///icium the pores are consider- 
ably less frequent and the border nearly one-half smaller. In 
Liriodendron aud Magnolia the pores are so few in number and 
the border so small that they may easily be mistaken for simple 
pores. The difference in regard to the number of elements was al- 
SO quite suggestive in these genera. In Drimys, where the borders 
are so large and so numerous, very few trachez occur, and none 
whose diameter exceeds that of the libriform cells. ///icium and 
Liriodendron contain a large number of trachea of different 
diameters and a smaller amount of wood parenchyma. These 
variations appear very striking when compared with the uni- 
formity found in other families. 
In conclusion, one more family. may be referred to, whose 
genera contain both simple and bordered elements in the libri- 
form tisssue in such variable quantities as to render it an excep- 
tion to most other families: this is Myrtacez. As before stated, 
