CHAP. I. 
INTERCELLULAR PASSAGES. 
31 
trivance to enable air to pass freely from one cavity to another. 
Alphonse De Candolle and Mohl consider the vessels of latex 
ef Meyer, or the vital vessels of Schultz, to be merely 
intercellular passages ; and this agrees best with the branched 
character which those vessels are said to possess. They are 
described by Schultz {Arch, de Bot, ii. 422.) as composed of 
tubes, slender, membranous, transparent, delicate, soft, flexi- 
ble, perfectly close, cylindrical when separated, angular when 
combined, susceptible of contraction, often communicating by 
branches or anastomoses, and containing a juice which is more 
or less thick and coloured. These tubes are said to be ex- 
tremely common ; to accompany the bundles of fibrous cellular 
tissue in the wood of both Exogens and Endogens; to be present 
either singly or combined in the cortical integument; and, fi- 
nally, to exist in roots, stems, leafstalks, flowerstalks, flowers, or 
wherever spiral vessels make their appearance. It may, perhaps, 
be supposed that these are instances of thin-sided woody tissue 
— and their so constantly accompanying the vascular system 
would seem to confirm that view ; — but I have never succeeded 
in discovering any sides to them. Their thinness is altogether 
at variance with the structure of the woody tissue in the 
plants where they are more particularly said to exist, and the 
figures of such tissue by Meyer (Phi/totomie, t. 10. yi 11. and 
t, 14. B. B.), together with the account given by Schultz of their 
shrinking and distending, to say nothing of the branching al- 
ready noticed, seem altogether to point to intercellular passages, 
and not to any special form of tissue. 
2. Of Receptacles of Secretion. 
But it frequently occurs that the simple intercellular pas- 
sages are dilated extremely by the secretions they receive, 
and either increase unusually in size, or rupture the coats of 
the neighbouring tissue ; by which means cavities are formed, 
replete with what is called the proper juice of the plant; that 
is to say, with the sap altered to the state which is peculiar to 
the particular species of tree producing it. Cavities of this 
nature are often called vasa -propria ; they are the receptacula 
sued of Link ; the vaisseaux propres of Kieser and De Can- 
