INTERCELLULAR SECRETORY RESERVOIRS. 445 



and occurring in stem and petiole either in the peripheral zones of parenchyma only, 

 and even within the hypodermal collenchyma, or also (Philodendron hastatum, tripar- 

 titum, micans) internally, between the vascular bundles. In the leaf-lamina they run in 

 the parenchyma between the tertiary branches of the bundles and parallel to them ; either 

 about the middle-plane of the leaf (e.g. Ph. micans, lacerum, crinipes, Imbe, &c.) ; or 

 near to the lower surface of the leaf, and only separated from its epidermis by 1-2 layers 

 of cells (e.g. Ph. eximium, Rudgeanum, Sellowianum, pinnatifidum, cannsefolium, &c.). 



The passages of Schismatoglottis, Homalonema rubescens, and H. Porteanum resemble 

 those of Philodendron in fundamental points of form and course, but with the limitation 

 that in the stem of H. rubescens, instead of elongated canals, there are found elliptical 

 cavities from 0-25™™ to 0.50™™ in length and 0-20™"! to 0-38™°^ in width. It is remark- 

 able that, according to Tr^cul's account, the canals and cavities are entirely absent in 

 H. Wendlandii. 



The parenchyma of the stem of Aglaonema marantaefolium is traversed throughout its 

 whole length by gum- (or mucilage-) passages about 0-24'**"* wide, which, however, are not 

 continued into the leaves nor into the peduncle. In A. simplex these are absent. 



Van Tieghem found similar gum-passages in the petiole and midrib of the leaves of 

 Monstera surinamensis, in the cortex of the stem, and in the petiole of Rhaphidophora 

 pinnata, and in the lower part of the petiole of Anthurium crassinervium, while they are 

 absent in M. Adansonii, Rh. angustifolia, and Anth. violaceum. 



The above-mentioned resin-passages have, as was above indicated, a typical structure; 

 in the roots of Philodendron their epithelium, which is composed of 2-3 layers, is 

 sheathed by 2-3 closely connected layers of narrow elongated sclerenchymatous fibres 

 (comp. p. 202). The resin-cavities in the stem of Homalonema are enclosed by several 

 layers of thin-walled cells arranged in radial rows (apparently derived by division from 

 so many primary cells) ; the inmost project uniformly in a convex manner into the 

 cavities. The gum-passages above mentioned are surrounded by a layer of small cells, 

 often projecting, as in the Marattiaceae, into the passage : these differ but slightly from 

 those of the adjoining parenchyma. 



In the rhizomes of the investigated species of Canna, and also in the lower portions of 

 the flowering stems, there are numerous passages : these are filled by a clear transparent 

 mucilage, which oozes out in glistening drops when they are cut through. The passages 

 are absent from the cortex, and are very numerous w ithin the periphery of the vascular 

 cylinder: in the middle they are less frequent. They traverse the rhizome longitu- 

 dinally, their endings have not been observed ; anastomoses and points of branching were 

 found here and there. Their walls are composed of small cells with abundant proto- 

 plasm, which often project as irregular papillae into the passage. There has been as 

 yet no thorough investigation of their development. 



Among the Compositw ' all investigated forms of the section TubiJlorcB have a system of oil 

 passages characterised by complexity of composition and uniformity of arrangement. 

 There are no investigations at hand concerning the Labiatijlorx. In the Ligulifloral 

 Cichoriaceae they are absent, with the exception of isolated cases to be mentioned 

 ultimately. 



In the roots of the Corymbiferee and Cynarea the passages lie in the innermost portions 

 of the primary cortex, and when typically arranged they form, a simple curved series 

 opposite each phloem group of the axile vascular bundle, thus alternating with two.xylem 

 plates of the latter. According to the usual plan of structure of the roots, the cells of 

 the inner layers of parenchyma are in these plants also arranged in regular radial and 

 concentric rows; between the angles of junction of any set of four there is a 4- or 3- angled 

 intercellular passage; the inmost layer has the properties of the endodermis. In the 

 simplest case the angular intercellular passages, lying at the point indicated between the 

 endodermis and the next outer layer of parenchyma, assume the properties (i.e. the 



Van Tieghem, Canaux Secreteurs, he. 



