Cavers : Xofes on Yorkshire Bryophytes. 



21 I 



by irreg-ular opening-s in the partitions, and ultimately with the 

 air by means of the pores in the dorsal epidermis. 



The EPIDERMIS, forming the upper limit of the green tissue, 

 consists of a layer of large cubical or oblong cells, which 

 usually contain very few chloroplasts and have their outer walls 

 thickened. The lateral walls are also thickened, especially at 

 the angles between adjacent cells (Fig. 2, D.). 



The PORES are narrow, but easily observed with a lens or 

 low power of the microscope. With a lens, each pore is seen 

 to stand on a slight prominence on the upper surface of the 

 thallus, and to be surrounded by a whitish rim. This rim 

 consists of five or six concentric rings of cells, each ring con- 

 sisting usually of six cells (Fig. 2, D.), which contain few or no 

 chloroplasts. The innermost ring bears a membranous ingrowth 

 of cellulose which is covered with fine grains of a waxy or 

 resinous substance. When water is placed on a fresh plant, 

 little or none of it is found to have entered the chambers, but 

 the latter are found to be waterlogged when the plant has been 

 previously soaked in alcohol, which dissolves the grains, so that 

 this coating apparently serves, as first suggested by Kn} '''^ in the 

 case of Marcliantia, to prevent the entrance of water into the 

 air-chambers. 



The VENTRAL TISSUE of the thallus is practically confined to ; 

 the midrib, being reduced to two or three layers or to a single 

 layer of cells in the wing on either side. In the midrib this 

 tissue consists of from 10 to about 20 layers of polygonal cells, 

 containing starch-grains (Fig. 3). Here and there we find single 

 cells almost filled by a large brownish oil-body. Similar bodies 

 occur in many other liverworts, both thalloid and foliose, and 

 they were first carefully studied by Pfeff"er, f who found that they 

 contain water, a proteid substance, oil, and in some cases tannic 

 acid, these constituents being mixed and forming an emulsion, 

 held together by an envelope of proteid matter. Later observers 

 (Kuster,^ Garjeanne||) have shown that each oil-body consists 

 of a proteid ground-mass in which the oil and other substances 

 are embedded, and the writer's observations agree with this. 

 In some cases these oil-bodies give the whole plant a charac- 

 teristic odour, which is especially marked in Fegatella, less so in 



* Bau und Entwickeluno^ von Marchantia polymorpha. (Aus deni Text 

 der Abth. 8 der ' Botanischen Wandtafeln.') Berlin, 1890 ; p. 369. 

 t Die Oelkorper der Lebermoose. Flora, 1874. 



X Die Oelkorper der Lebermoose und ihr Verhaltnis zu den Elaioplasten. 

 Inaug-. Diss., Univ. Basel, 1894. 



11 Die Oelkorper der Jung-ermanniales. Flora, 1903, p. 457. 

 1904 July 1. 



