i8o 



LECTURE XT. 



scales o{ Allitwi Cepa, A. fishilosim, etc., deserve mention ; they run somewhat close 

 beneath the epidermis, and consist of serially arranged, rather broad vesicles, the 

 ends of which communicate with one another by means of broad, pitted, transverse 

 septa, and they contain a granular coagulable latex, which flows out in some quantity 

 when a bulb is cut through at the base. The erroneously so-called laticiferous 

 vessels of the Maples (well developed in Acer plafanoides) are similarly constituted; 

 they run at the boundaiy between the phloem of the vascular bundle, and the 

 sclerenchyma strands accompanying it. The resin of the Co7ivolvulacece, partly 

 used in medicine (e. g. Scammony from the roots of Convolvulus Scammonium, 

 Jalap resin from the root of Ipomea purga), and others, are obtained, like the 

 dried latexes of the druggists' shops, by mere inspissation of the contents which flow 

 out in the form of latex from the serially arranged more or less elongated secretion- 

 vesicles of these plants. Like the true la- 

 ticiferous vessels, the rows of utricles men- 

 tioned may also be repeated in continually 

 increasing numbers in the secondary tissue, 

 originating from the activity of a cambium 

 ring. The same holds good of the short resin 

 and gum-resin vesicles found singly or in 

 small groups in the cortex ; and which are 

 distinguished by their refractive contents, 

 and occasionally by their considerable size, 

 in the Ginger-like plants, and in Calamus 

 {Acorns), Piperacese, Laurineae and INIagno- 

 liacese, and also in some Euphorbiaceae (Cas- 

 carilla bark) and Aristolochise. To these 

 forms are to be added the mucus-vesicles in 

 the parenchyma of the Malvaceae, Tiliacege, 

 Laurineae, Ulmeae, and species of Cactus, and 

 in the tubers of Orchis and the cortex of 

 the Pines. They are generally distinguished 

 from the ceils of the surrounding parenchyma 

 by their larger size ; and are filled with a gum- 

 like mucus, which dissolves in water. This 

 latter is in the majority of cases {according to 

 De Bary) nothing more than strongly swollen 

 cellulose, which fills up the lumen of the cell, and arises from alteration of the 

 cell-walls, still showing in part the layering and pitting of the latter. The mucus 

 in the tubers of Orchis (Salep) arises however, according to Frank, in the interior 

 of the protoplasm in the form of a vacuole, which grows up together with a small 

 bundle of raphides and presses the remaining contents aside. When, as in 

 Althea rosea, peculiarly grouped mucus-cells of this kind become completely 

 disorganised, there arise lacunae in the parenchyma of various shapes and sizes, 

 filled with this translucent mucus. Such gum-reservoirs are distinguished from the 

 cases of proper Gummosis, where large groups of tissue in the older organs are 

 changed into basorin and other kinds of gum (Cherry gum, Tragacanth, etc.), 



Fig. i8o.— Longitudinal section through a scale of the 

 bulb of Allium Cepa. e epidermis; c cuticle; / paren- 

 chyma ; sg^ the latex of the utricular vessel coagulated in 

 potash solution ; g q septum of the vessel. The longi- 

 tudinal wall is pitted, and separates the utricular vessel 

 from one lying behind. 



