496 SECOND ARY CHANGES. 



4. Vesiels, Woody fibres, Parenchyma, Intermediate fibres . 



(«) Both kinds of cells : Fraxinus excelsior, Ornus, Citrus medica, Platalius, &c. 

 (b) Only intermediate fibres : Viscum album. 

 {c) Only bundle-parenchyma: Avicennia. 



5. Vessels, Fibrous cells, Parenclyma. 



Cheiranthus Cheiri, Begonia. Here no doubt also belong many of the Crassulaces 

 and Caryophylleae which still need more minute analysis. 



6. Vessels, Fibrous cells. Parenchyma, Woody fibres (?). 

 Coleus Macraei, Eugenia australis, Hydrangea hortensis. 



7. Vessels, Tracheides, Woody fibres. Fibrous cells (septate), Parenchyma, Intermediate 

 fibres. 



Ceratonia siliqua, Bignonia capreolata, doubtful however as to the woody fibres 

 according to the existing data. 



Although no strict law holds good, without exception, for the distribution of these 

 tissues in the woods containing vessels, still certain general rules may be given. 



The vessels occur in all the layers of the annual ring, but are usually more fre- 

 quent in the internal than in the external portion. Only Bombax Ceiba shows the 

 opposite condition, according to Sanio. It is not uncommon, however, for their 

 frequency to show no difference from within outwards (Acacia Sophora, floribunda, 

 Enckea media, Artemisia Abrotanum) ; or only a slight one, the pores, or groups of 

 pores which they present in cross-section, being scattered uniformly through the wood, 

 e. g. Laurus nobilis, JEsculus, Acer, Populus. The vessels rarely form the main, 

 fundamental mass of the wood (Avicennia). As a rule they lie in small groups in the 

 non- equivalent fundamental mass, and these groups are either isolated or arranged in 

 more or less interrupted radial bands or concentric zones (Hedera Helix). They are 

 either everywhere of about the same width, or more usually their width is greater in 

 the inner part of the annual ring, and diminishes gradually or suddenly towards the 

 outside. With this difference in size, a difference in structure is in many cases also 

 united, in so far as the narrow vessels have spiral fibres, while the wide ones have 

 none (Morus alba, Broussonetia papyrifera, Gymnocladus, Virgilia lutea, Celtis aus- 

 tralis, Ulmus suberosa, Catalpa, and Robinia pseudacacia) ; or the structure is the same 

 in all (Quercus pedunculata, Castanea vesca, Fraxinus, Amorpha fruticosa, Sophora 

 j&ponica, and Periploca). 



In the above-mentioned ' parenchymatous ' woods, as Bombax, Carica, &c., and 

 also in the roots still to be discussed below, the bundle-parenchvma forms the main 

 mass in which the vessels and other elements are inserted in groups. In the solid 

 ' woody ' woods its arrangement has a regular relation to that of the vessels. 



It usually accompanies the latter, either in such a manner that it surrounds each 

 vessel or group of vessels singly — paratracheal parenchyma according to Sanio, e. g. 

 Enckea media; or it forms tangential bands, alternating with similar ones, con- 

 sisting chiefly of tracheides or fibres, in or at the side of which the vessels stand : 

 Sanio's metatracheal parenchyma. The latter, for example, is the case in the spring 

 wood of Tectona grandis, in the autumn wood of Fraxinus, in the autumn and spring 

 wood of Amorpha fmticosa, Sophora japonica, Robinia pseudacacia, Gleditschia 

 triacanthos, Gymnocladus, Virgilia, Caragana arborescens, Paulownia, Morus, Brous- 

 sonetia, Ailantus, Tamarix gallica, &c. In Casuarina equisetifolia, torulosa, Hakea 



