. The structure and development of mosses and ferns (Archegoniatae). re seldom by four or eight valves. The archesporiumdevelops sterile cells, in the form of elaters, as w^ell as spores. The Marchantiales constitute a very natural order ofplants, all of whose members agree very closely in their funda-mental structure. The separation of the Ricciacese as a groupco-ordinate with the Jungermanniales and Marchantiales is notwarranted, as more recent investigations, especially those ofLeitgeb ((7), vol. iv.) have shown that the two groups of theMarchantiacese and Ricciacese merge almost insensibly
. The structure and development of mosses and ferns (Archegoniatae). re seldom by four or eight valves. The archesporiumdevelops sterile cells, in the form of elaters, as w^ell as spores. The Marchantiales constitute a very natural order ofplants, all of whose members agree very closely in their funda-mental structure. The separation of the Ricciacese as a groupco-ordinate with the Jungermanniales and Marchantiales is notwarranted, as more recent investigations, especially those ofLeitgeb ((7), vol. iv.) have shown that the two groups of theMarchantiacese and Ricciacese merge almost insensibly into eachother. They are all of them strictly thallose forms, the thallusbeing unusually thick and fleshy, and range in size from a fewmillimetres in some of the smaller species of Riccia, to 10 to 20centimetres in some of the larger species of Diimortiera andConocephahis. In most of them branching is prevailingly 22 MOSSES AND FERNS CHAP. dichotomous, and as this is rapidly repeated, it often causes thethallus to assume an orbicular outline. Some forms, however,. 1structuredevelop00camp3
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