RESIN-PASSAGES, ETC. l8l 



in that they assume their characteristic condition at the beginning of the differen- 

 tiation of the tissues in the very young organs. Further are to be mentioned the 

 tannin-vesicles of many plants. These are isolated parenchyma cells, often hardly 

 distinguished in any other way, which are filled with a concentrated solution of tannin, 

 frequently accompanied by a red colouring-matter. Exquisite examples of them are 

 found in the cortex of the stem of the seedUng of Ricinus and many other germinat- 

 ing woody plants, where they attract the attention of the microscopist either directly 

 by the red coloiu-, or by forming ink on the addition of solutions of iron salts. 



A group of receptacles for secretions, well characterised anatomically, are the 

 resin-passages and gum-passages ; these arise by the separation of the walls of 

 neighbouring rows of cells, and thus constitute cellular passages filled with secre- 

 tions. In the Cycadese, some Lycopodioe, Marattiaceae, and species of Canna, 



Fig. iSr. — Part of the transverse section of the stem oi Fomiculitm ojfficiiiate (Fennel) slightly majrni- 

 fied. e epidermis ; <h ^een, and r colourless parenchyma of the cortex ; cc bundles of colienchyma ; hh 

 resincanals; A^wood;£'vessels; 7«pith. 



Opuntiae, and Araliaceae, these passages contain mucous substances ; in the Coniferse 

 (with the exception of Taxus) the contents are mixtures of ethereal oil and resin 

 (balsam), and the same also occurs in the Terebinthaceee, Umbelliferae and those 

 Compositae which possess no laticiferous vessels. These intercellular canals are 

 generally elongated, and often penetrate the whole of the organs of the plant ; 

 or they may be wanting in the roots, but are then so much the more abundant 

 in the primary and secondary cortex of the shoot-axes, and occur also in the 

 foliage leaves. The length of these canals, and apparently also their occasional 

 lateral communications, explain why trees which produce resin gradually exude 

 such large quantities of balsam from local wounds, which then generally stiffens 

 to pasty resinous masses in the air (resins of Coniferae, e.g. Sandarach, Mastic 

 derived from Pistacea terebinthus, etc.). In other cases, again, as in the AUsmaceae, 

 Butomaceae and the Aroideae among the Monocotyledons, and in the Clusiaceae, species 

 di Mamillaria, and Umbelliferae, among the Dicotyledons, such intercellular passages 



