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 - 

 of 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 thinnecs is altop-ether 

 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 {Phytotomie, t. 10. yi 11. and 

 1. 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 iwojiria ; they are the receptacula 

 sued of Link ; the vaisseaux propres of Kieser and De Can- 



