38o 



PRIMARY ARRANGEMENT OF TISSUES. 



cellj^. The border is in fact curved round the xylem in Sciadopitys, Araucaria 

 brasiliensis, Cryptomeria, and Dammara ; round the phloem in Abies pectinata and 

 Pinsapo. In Abies excelsa and the Pines (P. silvestris, Laricio) it is split as it 

 were into two plates on each side at its place of attachment, which, in a manner still 

 to be more accurately described, are bent, the one round the xylem, the other round 

 the phloem, so that the pair of bundles is completely surrounded by the border 

 of tracheides. 



The plates of tracheides are in many cases, especially in Podocarpus IMeyeriana 

 Endl., of nearly equal thickness throughout in every cross-section ; in the other 



Fig. 183. — Cunninghamia sinensis. Cross section through the leaf (220). u lower, o upper surface ; h resin 

 passage; xs sclerenchymatous fibres of the hypoderma, s those scattered in the parenchyma; g xylem of the median 

 bundle; / tracheide border of the latter. Below, towards the resin-passage, is the thin-n ailed phloem; the white 

 band at its boundary towards the parenchyma surrounding the resin passage is the compressed primordial tissue of 

 the phloem; g transversely elongated parenchymatous cell of the middle of the leaf. 



cases mentioned, except Abies excelsa and the Pines, they are thicker on their outer 

 edge, i. e. that remote from the vascular bundle, than on the inner attached edge, in 

 consequence of increase in the width and number of layers of their elements ; this 

 often takes place to such an extent that the cross-section becomes wedge-shaped, 

 e. g. Taxus and Podocarpus Thunbergii. 



The tracheides of the border are in general arranged in fairly regular rows both 

 in the direction of the length and of the breadth of the leaf; these rows often show 

 inierruptions, which are filled up by parenchymatous cells, but all are at some points 

 in immediate connection with one another. At the inner edge, which is attached to 

 the xylem of the bundle, their form is similar to that of the tracheides of the latter. 



