44 



MOSSES AND FERNS 



CHAP. 



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Small cells, each containing 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 (2). The 

 oil body has a round or oval form usually, and in the Mar- 

 chantieae 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 pres- 

 ent, and tannic acid. The latter is especially 

 abundant in the oil bodies of Lunularia, less so in 

 Marchantia and Preissia( Cavers (6) ; Kiister ( i ) ). 

 The thallus of the Marchantiaceae is made up al- 

 most entirely of parenchyma, but Goebel (3) 

 states that in Pre'issia commutata there are elon- 

 gated sclerenchyma-like cells in the midrib. The 

 walls of the large colourless cells of the lower lay- 

 ers of the thallus are often marked with reticulate 

 thickenings, which are especially conspicuous in 

 Marchantia. 



Most of the Marchantiaceae have no special non- 

 sexual reproductive organs, but in the genera 

 poly- Marchantia and Lunularia special gemmae are pro- 

 m o r p h a . duced in enormous numbers; and in the latter 

 tubercuiate form, which is extremely common in greenhouses, 

 r h i z o i d , the plant multiplies only by gemmae, as the plants 

 are apparently all female. These gemmae, as is 

 well known, are produced in special receptacles upon the dorsal 

 side of the thallus. The receptacles are cup-shaped in Mar- 

 chantia, and crescent-shaped in Lunularia, where the forward 

 part of the margin of the cup is absent. These cups are appar- 

 ently specially developed air-chambers, which, closed at first, 

 except for the central pore, finally become completely open. 

 The edge of the fully-developed receptacle is fringed. The 

 gemmae arise from the bottom of the receptacle as papillate 

 hairs, and their development is the same in the other two genera 

 where they occur. Fig. 13 shows their development in M. 

 polymorpha. 



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