INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC, 125 



Structure and Systematic Position of Ricciacese.* — Professor 

 Leitgeb's recent researches on this small group induce him to con- 

 sider them as forming a connecting link between the Jungermanniacese 

 and the Marchantiaceae. To the former belongs the section Rielleae, 

 including the genera JRiella and Splicer ocarpus, coming near the 

 Codoniete ; while the two remaining sections, the Corsiniese, including 

 Boscliia and Corsinia, and the true Riccicje, Riccia, Oxymitra, and 

 Ricciocarpus, must be classed under Marchantiaceae. The transition 

 is a gradual one, from the Eicciete, through the Corsinieaj, to the 

 MarchantiefB. 



As regards the alleged want of elaters, which has been supposed to 

 mark a clear distinction between the Riccicje and Marchantiaceas ; 

 with the exception of the lowest genera, Riccia and Oxi/mifra, all the 

 rest have sterile cells among the mother-cells of the spores, as has 

 long been known in the case of Sphmrocarpus and Riella. The 

 thickening of the wall of the capsule is also no good differential 

 character for the Marchantiace^, there being genera in that family 

 which do not possess it. Corsinia and Boschia are evident transitional 

 forms to^he Marchantiacese, the former with unthickened, the latter 

 with characteristically thickened elaters ; both genera approach that 

 family in the development of the archegonial receptacle, and in the 

 anatomy of the leaves. 



The three genera which make up the true Riccieae, Riccia, 

 Oxymitra, and Ricciocarpus, are characterized by the whole of the 

 fertilized oosphere becoming transformed into the capsule, without 

 any formation of a foot, and by the resorjition of the wall of the 

 capsule before maturity. Ricciocarpus {Riccia natans) is distinguished 

 by the antheridia being united into groups ; the ventral scales and 

 the anatomy of the thallus indicate an affinity to Corsinia. Riccia is 

 distinguished by its archegonia being buried in the thallus ; Oxymitra 

 by their being raised above its surface. 



The Corsinieae form rudiments of a foot even in the small-celled 

 embryo ; the wall of the caiisulo remains till maturity. 



Sphcerocarpus agrees with Corsinia in the formation of a foot, in 

 the persistent capsule-wall consisting of unthickened cells, and in the 

 occurrence of sterile cells among the mother-cells of the spores ; but 

 the anthcridial receptacle is wanting, and the development of the 

 embryo deviates greatly from that genus, and indicates an affinity 

 with the Jungermanniaccao through Fossomhronia. It is on the other 

 hand allied to Riella, in the identity of the earlier stages of develop- 

 ment of the embryo. Riella exhibits a special affinity to Jungerman- 

 niaccao in the structure and habit of the vegetative organs. The 

 " wing " of Riella is not equivalent to a longitudinal half of a shoot 

 of Marchantia, but is a " dorsal comb " or luxuriant growth of the 

 dorsal side of the stem. 



The question whether the sterile cells of the Riellca) must bo 

 regarded as rudimentary olatcr-cell^ of the Marcliantiaccao, or as 

 aborted reversions, Leitgob considers to be still unsettled. 



* ' UntersnohunRon iibcr die LebermooBO, von II. Loitgeb. Iloft 4. Dio 

 Riccieen. Grnz, lH70 ; sec ' Bot. Ztit.,' xxxvii. (1879) p. 629. 



