44 



MOSSES AND FERNS 



CHAP. 



which, arising at first from a single cell, rapidly increases in size, 

 and forms the overlapping dark purple marginal part of the 

 scale so conspicuous in many species. 



In different parts of the thallus are found large 

 mucilage cells, which are usually isolated, or in Cono- 

 cephalus, according to Goebel's ^ investigations, they 

 may form rows of cells which become confluent so 



as to form mucilage ducts. In the earlier 



stages 



Fig. II. — 7I/rtr- 

 chantia poly - 

 morplia (L.). 

 Part of a tuber- 

 culate rhizoid, 

 X52S- 



these cells have walls not differing from those of the 

 adjacent cells, but as they grow older the whole cell 

 wall is dissolved, and the space occupied by the row 

 of young cells becomes an elongated cavity filled 

 with apparently structureless mucilage. These cells 

 are recognisable at an early period, as their contents 

 are much denser and more finely granular than 

 those of the adjacent cells. Small cells, each con- 

 taining a peculiar oil body, are found abundantly in 

 most species, both in the body of the thallus 

 and in the ventral scales. The structure and 

 development of these curious bodies, which are 

 found also in many other Hepaticae, have been 

 carefully studied by Pfeffer.'-^ The oil body has a round 

 or oval form usually, and in the Marchantieae usually is 

 found in a special cell which it nearly fills. It is brown or 

 yellowish in colour, and has a turbid granular appearance. 

 The extremely careful and exhaustive study of these bodies 

 by Pfeffer has shown that the oil exists in the form of an 

 emulsion in water, and that in addition to the oil and water 

 more or less albuminous matter is present, and tannic acid. 

 The latter is especially abundant in the oil bodies of Lunularia, 

 less so in Marchantia and Preissia. 



The thallus of the Marchantiaceae is made up almost 

 entirely of parenchyma, but Goebel ^ states that in Preissia 

 conimutata there are elongated sclerenchyma-like cells in the 

 midrib. The walls of the large colourless cells of the lower 

 layers of the thallus are often marked with reticulate 

 thickenings, which are especially conspicuous in Marchantia. 



Most of the Marchantieae have no special non-sexual 

 reproductive organs, but in the genera Marchantia and 

 Lunularia special gemmae are produced in enormous numbers ; 

 1 Goebel (5), p. 531. 2 pf^ffer (2). 3 Goebel. 



