KESIN-PASSAGES. 



101 



more cells, but thej^ sometimes have a remarkable regularitj' 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. De Bary classifies these resin-passages and 



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

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

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

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

 qualit3^ in different cases ; a, passages or canals, as those in 

 Coniferse, Alismaceae, Aroidese, the tubuli-flowered Compositse, 

 Umbelliferae, Araliaceae, Anacardiaceae ; 6, short cavities, as in 

 species of Hypericum and the true Rutaceffi, many species of 

 Oxalis and Myrtaceae, and some species of Lysimachia. The 

 cells which surround the more complete cavities are so different 

 from the neighboring parenchyma that thcj- have been termed, 

 collectivelj', the epithelium of the spaces. 



It is not fully known in what waj- the various resinous and 

 mucilaginous matters are produced in the cavities. In some 

 instances, at least, the matters appear at a ver3' earl}' stage of 

 the development of the cells which are afterwards broken down 

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

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

 studjr, because they are so frequentlj- 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, sliowiiig a rcsin-passage, 

 HC. (Kny.) 



