SCLERENCHFMA AND SCLEROTIC CELLS. 419 



Fig. 27, p. 78). They form a thick uninterrupted layer on the upper side of the leaf 

 of Jacquinia ruscifolia, an often interrupted layer on the lower side of this leaf, and 

 on both sides of that of Theophrasta ornata and species of Olea. This form of the 

 strengthening apparatus is absent, however, in most leathery leaves, and in fact 

 this is the case even in such species as are closely related and similar to those 

 mentioned, e.g. most leathery leaves of Orchids, Pholidophyllum zonalum, Zamia 

 integrifolia, Taxus, Cephalotaxus spec, Tsuga Canadensis, Abies amabilis, &c. 



A continuous two- or many-layered fibrous investment further appears in the 

 aerial roots of Philodendron Imbe, Rudgeanum, and other species^. In the 

 Cyperacese, e. g. species of Carex, the outer layer of the cortex of the root is often 

 sclerotic in a high degree, and throughout many strata of cells. 



The second form of distribution of sclerenchymatous masses is that in which 

 they lie at a greater distance from the epidermis, in the inner regions, being united 

 so as to form either a continuous annular layer or isolated strands. 



The former arrangement occurs in a number of stems, in such a form that the 

 fibrous ring lies in the external cortex, bordering within and without on parenchyma- 

 tous layers : shoots of Berberis vulgaris ; Caryophylleae, as Dianthus plumarius, 

 Gypsophila altissima, Silene Italica; Cucurbitacese ; and climbing Aristolochise, as 

 A. Sipho ^. Usually, however, the fibrous layer lies on the outer border of the 

 bundle-ring or cylinder, in such a manner that it includes the vascular bundles, or 

 in the latter case the outermost of them, or that they rest against it. In this case, 

 and in Berberis ^, and doubtless also in the other plants mentioned with it, the ring 

 belongs, according to its origin, to the outer layer of the plerome, it marks, more or 

 less sharply, the outer boundary of the plerome. This phenomenon is of most 

 frequent occurrence in IMonocotyledonous stems. It occurs in the halm of many 

 Grasses and of many Cyperaceae and Juncacese, and in fact sometimes in combina- 

 tion with the occurrence of hypodermal fibrous ridges, which, as processes of the 

 ring, unite the latter with the epidermis, e. g. Piptatherum, Molinia, Bromus spec. * ; 

 or penetrate from the outside close up to the ring without reaching it (Alopecurus 

 pratensis, Panicum turgidum, Juncus paniculatus) ; or, lastly, show sometimes one, 

 sometimes the other condition (Cladium Mariscus). Other plants belonging to the 

 families mentioned show the sclerenchymatous ring connected only with isolated 

 ridges of the epidermis, or without this connection, and only with projecdng ribs, which 

 correspond to the insertion of vascular bundles, on its outside ; e. g. Rhynchospora 

 alba, Juncus bufonius, Pennisetum longistylum. To the latter cases is related the 

 smooth and sharply limited sclerotic ring, which, with numerous individual modifica- 

 tions, forms the outer boundary of the cylinder, and includes or supports the 

 peripheral vascular bundles in most Monocotyledonous foliage-stems : Restiacese, 

 Eriocaulonege paitly, Commelinese, JMelanthaceae, Liliaceaj, Smilace^, Tamus, Iride^e, 

 Orchideas, Alismacese, Typhacese, &c. ; and in most rhizomes, also belonging to the 

 families mentioned above. 



The same phenomenon of a sclerenchymatous ring directly supporting or 



' Van Tieghem, Struct, des Aioidees, /. c. 



^ Compare Trevirauiis, Physiol. I. p. 209. — Caspary, Pringsheim's Jahrb. I. p. 444. — Sanio, 

 Botan. Zeitg. 1864, p. 222.— Von Mohl, Palm. Struct. Tab. H.— Mettenius, I.e. 



•' Compare Schmitz, /. <. (p. 393). * Compare Schwendener, I.e. 



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