3.5^ MUSCINEM. 



in this manner attained its destined height, and partially even at an earlier period, 

 a number of divisions of different kinds take place by which the structure is com- 

 pleted. The wall of the sporogonium becomes differentiated from the tissue from 

 which the mother-cells of the spores are to arise ; if elaters are formed they originate 

 from the same tissue, the cells -ceasing to divide transversely at an earlier period 

 and remaining long, while the intermediate cells become rounded off and give 

 rise to the mother-cells of the spores (Hofmeister). 



The mode of division into four of the mother-cells of the spores also 

 varies. Those of Anihoceros form at first two, and afterwards four, new nuclei 

 which are arranged tetrahedrally, the protoplasm dividing before the nucleus ; cell- 

 walls are then formed, and thus the mother-cell breaks up into four spores \ In 

 Pellia and Frullania^ on the other hand, the division of the mother-cells commences 

 by four protuberances arranged tetrahedrally, which at length are cut off by cell- 

 walls; each contains a nucleus, and they form as many spores; in Pellia the spores 

 immediately again divide several times, and thus give rise to a young plant. 



The Hepaticae are usualy divided into five families, viz.: — 



1. Anthoceroteae, 



2. Riccieae, 



3. Monocleae, 



4. Marchantieae, 



5. Jungermannieae, 



of which the first four include only thalloid forms, the fifth both thalloid and foliose 

 genera. 



I. AnthocerotesB. Anthoceros IcB^vis said punctatus, which grow in summer on loamy 

 ground, develope a perfectly leafless flat ribbon-like thallus, its irregularly developed 

 ramifications forming a circular disc ; the regularity of the dichotomous branching is 

 disturbed by the adventitious shoots, which proceed from the margin of the thallus, and, 

 in A.punctatus, also from the upper surface. The thallus consists of several layers of 

 cells, and the apical cells of the branches which lie in the anterior depressions are 

 divided by walls inclined alternately upwards and downwards (Fig. 237, C). In each 

 of the cells of the thallus, the upper layer of which does not become differentiated 

 into an epidermis, only one chlorophyll-granule is formed, surrounding the nucleus. 

 On the under side of the thallus, Janczewski states that stomata are formed close behind 

 the growing margin, through which filaments of Nostoc frequently penetrate, forming 

 roundish balls in the tissue of the thallus (Fig. 237, B), which were at one time considered 

 to be endogenous gemmae'^. The antheridia and archegonia arise apparently without 

 any defilnite arrangement in the interior of the upper side of the thallus. The formation 

 of the antheridia commences by a circular group of cells of the outer layer separating 

 from the subjacent tissue and thus producing a broad intercellular space, several of the 

 lower bounding cells of which, after some vertical divisions, rise up in the form of 

 papillae, and form the antheridia (Fig. 237, 5, ««). It is only when the chlorophyll- 

 granules in the walls of the antheridia have assumed a yellow colour and the anther- 

 ozoids are mature that the roof of the cavity is ruptured, the antheridia opening 

 at their apex and allowing the antherozoids to escape. In the Riccieae and Mar- 

 chantieae the archegonia, which are at first free, become gradually surrounded by masses 

 of tissue, but in Anthoceros they are enclosed from the first. One of the superior 



^ [On the development of the spores of Pellia and Anthoceros see Strasburger, Zellbildung und 

 Zelltheilung, 3rd ed. p. 156.] 



2 [See Waldner, Ueb. die iVos/oc-Colonieen bei Blasia, Sitzber. d. Wien. Akad. 1878,} 



