472 Researches into the Anatomy of Plants. 
organs which resemble them much externally, although 
they are merely a Jongitudinal excavation in the form of a 
vessel, made in the cellujay texture or in the wood of the 
plant. Such are the vessels proper of several of the Conz- 
fere which run through the bark, and also the wood of 
these trees. We even find them in the wood of the same 
year: itis clear therefore that they prove nothing for the 
change of the bark into wood. The vessels proper of the 
Rhus and of the Schinos belong to this class. As the name 
of vessels does not exactly suit them, T would call them re- 
servotrs proper of the sap. 
The sap certainly passes by the membranes of the fibrous 
vessels, or by the partitions of the cellular texture in order 
to reach the vessels and reservoirs proper of the sap. It is 
a continual fijtration which changes and prepares the sap. 
The secretion takes place in the plant in the simplest man- 
ner, the slackening and constriction of the membranes are 
the means resorted to by nature to produce these changes. 
The air of the tracheze contributes to them by oxidation 
or de-oxidation, and perhaps the organs of the plant are 
galvanic machines, similar to the electrical organs of some 
fishes, which seem to be composed of nothing but cellules 
placed by the side of each other. 
There are excavations in the plants which are empty or 
rather filled with air. Mirbel calls them Lacune ; a very 
correct expression, because they are generally the conse- 
quence of age. The differences in these Lacune may be 
reduced to the following classes. 
1. Lrregular Lacune. They are to be found in the heart 
of the leaves; the receptacles of fruits and some other parts 
which contain abundance of cellular texture. 
2. Fistulous Lacune. They occupy the middle of the 
stalk, the branches, the petiole and the peduncles; they 
are formed by age. 
3. Regular Lacune. In some aquatic plants, the cellules 
in the middle of the stalks are separated from each other, 
and arranged in a regular and sometimes very elegant 
manner. The stalks of the Scirpus palustris, S. maritimus, 
and of the Sparganium erectum exhibit examples of this. 
4. Cellular Lacune. When the stalk of some aquatic 
plants (as the Sparganium erectum) is cut, large cellules 
are visible to the naked eye. 
The Lacunz supply the place of the trachez, and carry 
the air where it is wanted. They are not accidental, but 
‘necessary organs of vegetation, 
V. Pores 
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