32 CELLULAR TISSUE. 



or nerves, and the spaces between these ; it is a general rule, that here the epidermal 

 cells over the stalk and ribs are longitudinally extended, and with straight sides, but 

 between the ribs the form and direction of the predominant elongation often alter ^j 

 further differences occur in relation to thorns, prickles, teeth, &c. The leaves 

 with stomata airanged together in groups (Begonia, Saxifraga sarmentosa) will 

 be noticed below. 



(i3) Independent of relief, and of distribution of stomata and hairs. To this 

 category belong a number of very different special cases. In the bands of epidermis 

 free from stomata of the leaves and green stems of most Graminese the epidermis 

 consists of longitudinal rows of cells, of which some are elongated; others, 

 alternating pretty regularly with these, are short, that is, broader or at most as 

 broad as they are long. The short ones stand singly or by twos or threes between 

 two long ones; in the two latter cases a further inequality often occurs, in that 

 the upper, or as the case may be the middle cell differs in form and structure 

 from the others'*. 



In the bands of epidermis, without stomata, which cover the peripheral 

 bundles of fibres in the stem and leaves of the Cyperaceae, Douval-Jouve found one 

 to two longitudinal rows of epidermal cells distinguished from the rest by a less 

 prominent outer wall, and instead an inner wall projecting inwards in form of a 

 strongly thickened cone ". 



The cystoliths scattered in the epidermis of the Urticaceae and Acanthaceae 

 (Sect. 2i), the elongated sac-shaped cells rich in tannin scattered or arranged 

 in rows between the isodiametric sinuous elements which Engler* found in the 

 epidermis of Saxifraga cymbalaria and its allies and of Sedum spurium, the 

 large solitary cells in the small-celled epidermis of the leaf of Cymodocea nodosa, 

 and rotunda", are to be registered as further kindred peculiarities. Then the 

 •Interstitial-bands' on the under side of the lamina, between the nerves of the 

 floating leaves of most if not all species of Marsilea, must be mentioned. They 

 consist of at most three to five rows of epidermal cells, which are distinguished from 

 the ordinary cells with undulating colourless walls by more elongated form, smaller 

 size, deep golden-brown colour of the wall, and homogeneous fluid contents. Many 

 appearances, to be described below with glands and hairs, are directly connected 

 with these. 



i. An epidermis, more than one layer of cells thick', appears in the simplest caseSj 

 by the division of each original epidermal cell by one or more tangential walls into 

 Chambers, which exactly fit one on another. In many cases this happens one 

 may almost say casually to single cells, while the neighbouring cells, which resemble 



' Compare Kiaus, /. c. p. 309. 

 ; ^ Compare Bot. Zeitg. 1841, p. 149, pi. I. figs. 10, li (Coix), 12 (Sorghum),— Pfitzer, Pringsh. 

 Jahrb.VII. p. 555. Here the descriptions of the older writers and the discovery by Treviranus(Veim. 

 Schr. II) and Meyeu (Phytotomie, p. 312, Taf. III. 2, 3) are cited. 



' Douval-Jouve, in Mem. de I'acad. de Montpellier, 1872, p. 227. The phenomenon appeared 

 in all the species of the family which were investigated, i. e. of the genera Cladium, Rhynchospora,. 

 Fuirena, Eriophorum, Schomus, Scirpus, Galilea, Cyperm, Carex, Kyllingia, Hypolytrum, Diplasia. 



* Botan. Zeitg. 1 871, p. 886. 



° Magnus, ibid. 1871, p. 210. 



« Treviranus, Verm. SchrifteUj IV. p. 11.— Pfitzer, in Pringsh. Jahrb. VIII. p. i6, Taf. VI. 



