208 



SOME POINTS 

 IN THE BIOLOGY OF HEPATIC/E. 



K. CAVERS, H.Sc, 



(Coiuimici.1 from 'The Naturalist,' May lyo.?. p. 176.) 



Marchantia and Luniilaria grow chiefly in open but moist 

 situations, where there is Httle daiig'er of complete drying- up. 

 They have hirge air-chambers with wide pores, the epidermis 

 contains chlorophyll, and the ventral scales and root-hairs are 

 well developed. In these forms, as in Fegatella, the thallus is 

 not adapted to withstand desiccation ; if left dry for a few days 

 the plants wither and die. The structure of the thallus varies 

 considerably with varying- conditions oi the environment as to 

 lig'ht and moisture. The influence of lig'ht on the thallus- 

 structure was pointed out by Stahl, and may be readily observed 

 if young plants are raised from gommiL', some being- set in direct 

 sunlig-ht, others in more or less deeply-shaded places. The 

 plants that receive the greatest amount of light show the 

 thickest thallus, the air-chambers being- well developed and con- 

 taining- nimierous branched g-reen filaments, and the epidermis 

 beings thick and nearly colourless. In plants exposed to diffuse 

 lig'ht the thallus is thinner, the chanibers shallower, and the 

 epidermis having- abundant chlorophyll. Finally, young- plants 

 kept in deep shade show no air-chambers or very shallow ones, 

 and the thallus is green throughout. Observations in the field 

 g-ive analog-ous results, though the diflferences between the 

 shaded and the exposed plants are not so sharply marked as in 

 the cultures of g-emma;. Sometimes in examining- patches of 

 MiDchautia, Liiiiulnria, and Fcgtik'/Id which are gfrowing beside 

 streams, we find parts of a patch becoming- submergfed in the 

 water. These submerged parts are long^ and narrow, the scales 

 and root-hairs are poorly developed, and the air-chambers show 

 a g-radual reduction in size and often disappear altog'ether. 

 This leads us to the consideration o'i two rare British forms 

 which occur in very moist and deeply-shaded situations, namely, 

 DuDiortiera irrigua and Cyathodium cavernarum. In the former 

 air-chambers are absent from the older parts of the thallus ; 

 chambers are laid down as usual at the g-rovving-point, but they 

 later become disorgfanised. In exotic species of Z)«W6>/-//W7'« no 

 traces of chambers can be detected at all, but in D. hirsuta the 

 epidermal cells gfrow out to form short green filaments. In 



Naturalist, 



