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ANATOMY, AND LIFE-HISTORY OF THE CONIFEBJE. 253 



The Endoderm. — The mesophyll is limited on the inner side 

 by the endoderm or bundle-sheath, consisting of a single row of 

 oval cells, sometimes more or less thickened by collenchymatous 

 deposit at the points of contact. The endoderm is usually very 

 well marked in species of Pinus, Abies, and Picea, while in Phyl- 

 locladus, Podocarpus, Dammar a, Fitzroya, Juniperus, and Sciado- 

 pitys it is generally ill-defined. 



The Pericycle. — The endoderm immediately encircles the peri- 

 cycle, which is composed of parenchymatous tissue of varying 

 amount, destitute of chlorophyll, but often containing starch 

 [probably always at some stage of their existence]. These cells 



intermixed 



very 



matous cells. In those cases where the fibro- vascular bundle 

 remains unbranched the pericycle is cylindrical, circular in out- 

 line as seen in section, e. g. Pinus Lambertiana, Pseudolarix 

 Kampferi, Picea spp., &c, &c. ; but if the bundle is double, i. e. 



divided, then the pericycle is transversely oval or reniform in 

 section. 



The Fibro-vascular Bundle. — The centre of the pericycle is 

 occupied by the fibro-vascular bundle. In most cases there is 



but 



( 



as in Araucaria, there are several such bundles traversing the leaf, 

 each with its own pericycle and forming several ribs. 



The central bundle is usually undivided throughout its course, 

 but sometimes it bifurcates, and then on a transverse section an 

 appearance is presented as of two bundles, often separated at 

 the dorsal side by a wedge-shaped mass of thick-walled cells ; so 

 that the two divisions of the bundle, instead of being in one 

 transverse plane ( ), are now inclined (/ x ) 





i 







In Pinus rigida and some others the masses of xylem, instead of 

 pointing upwards and inwards, point outwards ( x /), diverging 

 from the base. 



The central bundle consists of phloem elements on the outer 

 or dorsal side and xylem on the inner side. In Sciadopitys the 

 relative position of these elements is reversed. 



The phloem-cells are more thin-walled than the xylem-cells, 



the mass of which latter presents in section a wedge-shaped out- 



lne > ^e base towards the phloem, the truncated apex towards 



the centre and upper side of the leaf. The xylem-cells are usually 



packed in regular series, so that on section the rows seem to 





IMHr. JOUBN. — BOTANY. VOL. XXVII. T 



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