ox I'HE AXATOMY OF MAGXOLTAOE^E. J 33 



ß.orcC) ; but not in Lirioderulron. Development of cork seems to take 

 place in these genera immediately under the epidermis. The hypoderma 

 is generally represented by a layer of thick-walled parenchymatous 

 cells which are packed very closely (PL V., Fig. 22, hp). The cells 

 constituting the hypoderma are in some cases transformed into 

 scleroblasts, as is seen in Magnolia (frandifl ova ^ hijpoleuca (PI. Y, Fig. 28, 

 ///)), piiniila, imrvißora^ &c. Resin-sacs are scattered about in the ex- 

 ternal cortex. Each consists of a cell having a form similar to that of 

 the surrounding parenchymatous cells, but distinguished from these by 

 the nature of its contents, the thickness of its wall, and also in most 

 cases bv its size. These sacs are conspicuous in Magnolia and Lirioden- 

 dron, ])ut hardly so in Miclielia. In many species they are found in the 

 phloem, and even in the pith. The contents of these sacs are probably 

 the chief source of the aroma possessed by the species of these genera. 

 Like that of the resin-sacs the occurrence, either singly or in groups, 

 of scleroblasts in the external cortex is universal in these genera, 

 These cells are, however, very rare in some species, e. g., Magnolia 

 pa rri flora. Some of them are many armed and may properly be 

 called trichoblasts. 



- The sclerenchymatous fibres are greatly develo])ed, and not only 

 form a sfroug sheath to the fibro-vascular bundles, l)ut arc found 

 mixed among the soft bast. A few scleroblasts are also found with 

 the sclerenchymatous fibres that lie at the external limit of the phloem, 

 and with them constitute an almost continuous sheath. The phloem 

 portion consists of the usual elements. The xylem contains the 

 trachea3, filn'ous elements, and wood-parenchyma. The vessels present 

 bordered ])its in their walls. Tlie medullary rays vary in breadth, 

 some consisting of three or four rows of cells, and others of a single 

 row. Sclerenchymatous elements are generally absent in the phloem 

 ravs. 



