304 



HEP A TIC IF.. 



gonium. Those cells of the layer surrounding the columella which are to become elaters' 

 undergo either one or several additional vertical divisions ; the elaters are in this case 

 transverse rows of cells in which no spiral bands are formed. The intermediate cells 

 become rounded off and isolated progressively from the apex to the base of the spo- 

 rogonium ; and after they have still further increased in size, the division commences 

 into four spores arranged tetrahedrally. The sporogonium extends and forms a pod 

 some 15 or 10 mm. in height, the brown wall of which splits into two valves from 

 above downwards. 



2. The family Monocleae appears, according to the 'Synopsis Hepaticarum,' to 

 contain transitional forms between the Anthoceroteae and the Jungermanniese. The 

 long sporogonium has a longitudinal dehiscence and no columella ; and the sexual gene- 

 ration is either thalloid or foliose. 



^. The E-iccieee form a flat dichotomously branched but thalloid stem, floating in 

 \vater or rooting in the ground, the apical cells of w^hich, lying close to one another 

 in the anterior depressions of the branches, are stated by Kny to become multiplied by 

 vertical longitudinal partitions, and segmented by walls inclined upwards and down- 



FIG 218 —Ricciaglciiica; A vertical longitudinal section through the apical region ; s apex, * leaves, a yoiinsr anthe- 

 ridium, a' older antheridium already surrounded by involucral tissue w ; B rudiment of an antheridium a already 

 overarched ; C young antheridium a in longitudinal section (after Hofmeister, X500). 



\vards\ On the upper side a distinct epidermis is differentiated, but without stomata, 

 and beneath this lies the green tissue often provided with air-cavities, which is de- 

 rived from the upper segments of the apical cells ; the under side is provided with a 

 single longitudinal row of transverse lamellae, which, resulting immediately from the lower 

 segments of the apical cell, must be considered as leaves. Afterwards they split length- 

 wise and form two rows ; between them arise a number of root-hairs wnth conical thick- 

 enings projecting inwards. 



The archegonia and antheridia are formed on the upper side from young epider- 

 mal cells which grow^ into papilla;, and are overarched, in consequence of their mode of 

 development, by the surrounding tissue (Fig. 218). This involucre sometimes forms 

 an elevated neck above the sessile antheridia. The archegonia project, at the time of 

 fertilisation, above the epidermis ; subsequently they are arched over, and develope from 



1 In a letter on the apical growth of Blasia, Leitgeb shows that this Liverwort possesses only 

 one four-sided apical cell. He remarks: — 'I entertain no doubt that in Hepaticse also, which, 

 according to Kny, have a row of apical cells (Pellia, Riccia), only one apical cell is really present, 

 which divides as in Blasia. The deception may result from the lateral segments forming their 

 first divisions in the same manner as the apical cell, by the formation of segments standing fore 

 and aft. This led to the conclusion that the observer had before him in fact a row of apical cells.' 



