349 



If HEP A TIC M. 



ir dioeciously. There is a general tendency in the thalloid Hepaticae for the 

 exual organs to be depressed into hollows by overarchings of the surrounding tissue, 

 often opening externally by only a narrow mouth. An example of this is given in 

 Fig. 235. 



In the foliose Jungermannieae the origin of the antheridia and archegonia is 

 very various, and they are also enveloped in different ways. Further reference will 

 be made to this in describing the different families. 



The antheridium consists, in the mature state, of a pedicel surmounted by 

 a globular or ellipsoid body; in those which are imbedded in the tissue the former 

 is usually short, in the free forms it is long, and com- 

 posed of from one to four rows' of cells. The body 

 of the antheridium consists of a wall formed of a single 

 layer of cells containing chlorophyll ; the whole of the 

 space enclosed by it is densely filled by the mother- 

 cells of the antherozoids ; their escape is occasioned 

 by the access of water and separation of the cells of 

 the wall at the apex ; sometimes, as in Fossombronia, 

 these cells even fall away from one another. The 

 small mother-cells of the antherozoids which escape 

 in great numbers, separate in the water; the anthero- 

 zoids become free, and have the appearance of slender 

 threads curved spirally from one to three times, and fig. 235.-Anterior margin of the youn? 



.JJ..1 .. j'ili 1 n antheridial disc of Marchantia polymor- 



provided at the anterior end with two long very tine pna; a the growing margin; a, a. a the 



.,. 1 c ^ ' \ ,-\ • .!_ i. '1.1 antheridia in different stages of develop- 



Cllia, by means 01 which they move m the water with ment : ^Z the stomata above the air-cavltles 



. ,. ,. TT 11 o J /v ^1 i between the antheridia (after Hofmeister, 



a rotating motion. Usually they drag after them at X300). 



the posterior end a small delicate vesicle, the origin of 



which Strasburger traces to the central vacuole in the protoplasm of the mother-cell, 



in the periphery of which the antherozoid has been formed. 



The succession of cell-divisions in the formation of the antheridia has been 

 shown by the researches of recent observers to present great diversities in the 

 different genera; they agree, however, in the antheridium always making its first 

 appearance as a papilliform swelling of a cell from which it is separated by a 

 septum. This papilla thus detached again divides into a lower and an upper cell, 

 the former of which produces the pedicel, the latter the body of the antheridium 

 (parietal layer and mother-cells of the antherozoids). 



The succession of cell-divisions in the formation of the archegonia, from the 

 observations of Janczewski*, Leitgeb, Kny, and Strasburger, appears to be essentially 

 the same in the different families, even, mutatis mutandis^ among the Anthoceroteae. 

 It is certain that the archegonium, like the antheridium, makes its first appearance 

 as a simple papilla, which, in the case of the first archegonium of a receptacle 

 of Radula^ is itself the apical cell of the shoot. This papilla is shut off by a septum, 

 and, in Riccia^ is at once the mother-cell of the whole archegonium : in the other 

 Hepaticae it is divided by a second septum into two cells, the lower one of which 



* [Janczewski has made a series of comparative researches into the development of the arche- 

 gonium of Muscinese, Bot. Zeitg. 1872, p. 869 et seq.] 



