IIEPATICAE. 



149 



Other thalloid forms, as has been ah-eady said, protect the sexual ori;ans by sinking 

 ihrm in cavities produced by the more rapid growth of the tissue immediately 

 around them, and which often have only a narrow opening to the outer air. Fig. 99 

 is an example of such cavities. 



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

 very various, and the organs in these also have different forms of envelope ; about 

 which more will be found in the detailed descriptions of the different families. 



The an/heridiu/n in its mature state consists of a stalk and the spherical or ellip- 

 soid body ; the former is usually short if the antheridium is sunk in the tissue, 

 longer if it is free, and is composed usually of from one to four rows of cells. The body 

 of the antheridium consists of a wall of one layer of cells, containing chlorophyll ; the 

 whole of the space enclosed by it is densely filled with the mother-cells of the sperma- 

 tozoids, which are discharged when water finds its way into the antheridium by the 

 parting of the cells of the wall at the apex, or sometimes, as in Fossombrotiia, by the 

 entire separation of these cells from one another. 

 The small spermaiozoid-mother-cells discharged at 

 intervals and in great numbers from the antheridium 

 become isolated in the water, and the spermalozoids 

 issue from them as slender threads from one to ihree 

 times spirally twisted, and wiih two long and very 

 delicate cilia at the anterior extremity, by means of 

 which they move about in the water and turn on 

 their own axis; they usually drag a small and delicate 

 vesicle attached to their hinder end. The develop- 

 ment of the spermatozoids agrees, as far as we at pre- 

 sent know, with that described by Schmitz in Nitella 

 and elsewhere^; that is, they are formed chiefly from 

 the nucleus of the mother-cell, which grows more 

 dense towards the circumference and splits up into the 

 screw-thread of the spermatozoid, while the central 

 and looser part forms the vesicle above mentioned. 



The order in which the cell-divisions follow one another in the formation of the 

 antheridium varies, according to the statements of observers, in the different genera ; 

 but in all the first rudiment is always a papillose protuberance on a cell, the papilla 

 being then separated by a transverse septum. The papilla thus separated divides 

 into a lower and an upper cell ; the former produces the stalk and the latter the body 

 of the antheridium, that is the wall-layer and the spermatozoids ^. 



The order in which the cell- divisions follow one another in the formation of the 

 archigonium is essentially the same in the different families. Like the antheridium the 

 archegonium first appears as a papilliform outgrowth of a superficial cell, which, in 

 the case of the first of a group of archegonia in Radiila, is the apical cell of the shoot. 

 The papilla is cut off by a transverse septum, and in Riccia is at once itself the 

 mother-cell of the whole archegonium ; in other species it first divides transversely 



Fig. 99. Anterior margin of the young 

 male cap-like sexual slioot of Marchantia 

 foty7norpha ; r the growing margin \ a^a^a 

 the antheridia in different stages of their 

 development ; sp the stoniata over the air- 

 cavities between the antheridia. After Hof- 

 meister, magn. 300 times. 



' For Pellia see Goebel, loc. at. 



^ [Satter, Beitr. z. Entwicklungsg. A. Lebermoos-Aiitheridiums i.Sitz. d. K. Acad. d. Wiss. 

 Wien, 1852).] 



