1 70 Cavers : Some Poiiifs iti the Biology of Hepaticce. 



spot, found on closer examination to mark the position of a pore 

 which leads into an underlying air-chamber. An allied form, 

 common!}' found ofrowing in large patches on stones beside 

 streams, is Fegatella conica, readily distinguished from Mar- 

 cJianfia and Ltniiilaria by the fact that the surface-marking of 

 the thallus is much more distinct, both the areas and the pores 

 lacing wider (Fig. i). Fegatella conica is of historical interest, 

 being the form to which Micheli in his 'Nova plantarum genera,' 

 published in 1729 at Florence, gave the name Hepatica foil tana , 

 the generic name being suggested by a supposed resemblance 

 between the branching ribbon-like thallus and the lobes of the 

 liver. The statement, which has been handed down in many 

 books even to the present day, that Marchantia and its allies 

 are of medicinal use in liver complaints, apparently originated in 

 an application of the old adage, ' similia similibus curantur. ' 

 The Hepaticce are, from the economic point of view, an entirely 

 useless group of plants, but to the student of plant-evolution 

 they form perhaps the most important group of all, a group 

 wliich is above all an extremely generalised and ill-defined one 

 and includes forms showing a remarkable range in regard to 

 structural complexity. The Hepaticae occupy a unique position 

 in the vegetable kingdom, serving as a connecting-link between 

 the Algai on the one hand and the Vascular Plants on the other. 

 One of the most convenient forms with which to begin a 

 study of the biology of the HepaticcE is Pellia, which is very 

 widely distributed in this country, usually forming large patches 

 on the banks of streams. The green, flattened, ribbon-like 

 plant-body or thallus is attached to the soil by numerous colour- 

 less or reddish root-hairs. Its upper surface is smooth, not 

 showing the pattern observed in the forms already mentioned ; 

 it is usually from ten to about fifteen cells in thickness along the 

 middle line, the broad midrib passing gradually into the thinner 

 lateral wings, which become reduced to a single layer of cells at 

 the margin. The thallus consists throughout of compact tissue, 

 the upper layers being- made up of chlorophyll-bearing cells, 

 whilst the lower layers are colourless ; there is, however, no 

 sharp limit between the green and the colourless regions. Two 

 species of Pellia are abundant in Britain, and it is sometimes 

 difficult to distinguish these when in the sterile condition, 

 unless sections of the thallus are examined. In P. epiphylla, 

 which is monoecious, many of the cells of the thallus have their 

 walls strengthened by broad thickened bands, yellow or brown 

 in colour ; P. calyciita, which is dicecious, does not show these 



Naturalist, 



