RESIN-PASSAGES. 



101 



more cells, but the}' sometimes have a remarkable regularity ol 

 form and clearness of outline. 



It has been observed that these spaces filled with resinous and 

 other matters are not, as a rule, met with in the plants which are 

 provided with the simpler receptacles, consisting of single cells 

 or small groups. Ue Bary classifies these resin-passages and 



82 



spaces as follows: (1) those passages which contain mucilage 

 and gums, as those in the Cycads, species of Canna, Opuntia, 

 and some Araliaceae ; (2) resin-canals and cavities containing 

 resins, ethereal oils, emulsions of resinous gums, etc., variable in 

 quality in different cases ; , passages or canals, as those in 

 Coniferce, Alismaceae, Aroideae, the tubuli-flowered Composite, 

 Umbelliferse, Araliaceae, Anacardiaceae ; ?>, short cavities, as in 

 species of Hypericum and the true Rutaceae, man}' species of 

 Oxalis and Myrtacea?, and some species of Lysimachia. The 

 cells which surround the more complete cavities are so different 

 from the neighboring parenchyma that they have been termed, 

 collectively, the epithelium of the spaces. 



It is not fully known in what way the various resinous and 

 mucilaginous matters are produced in the cavities. In some 

 instances, at least, the matters appear at a very early stage of 

 the development of the cells which are afterwards broken down 

 to form the cavity. The special cases, like those of the Myrta- 

 ceae, in which the cavities contain oil, are best for purposes of 

 study, because they are so frequently to be found in the thinnest 

 leaves, and at an early stage of development. 



FIG. 82. Transverse section of part of leaf of Pinus Laricio, showing a resin-passage, 

 HC. (Kny.) 



