174 Cavers: Some Points in ilic Biology of Hepaticcc. 



arrang-ed in several tiers and separated by thin partitions (Fig-. 3). 

 Each of the uppermost chambers opens by a pore, whilst the super- 

 posed chambers communicate with each other by means of 

 small pores in the partitions. The sterile floating plants bear 

 no root-hairs, but are provided with numerous long- strap-shaped 

 scales which hang- down into the water. The terrestrial fruiting 

 form of ^. nutans is, however, provided with root-hairs, and the 

 ventral scales become fewer, shorter, and broader, whilst the 

 air-chambers are less developed than in the aquatic form, 

 the compact ventral tissue increasing in thickness at the expense 

 of the upper spongy tissue. In the case of Ricciella Jiuitans 

 the result of transferring the aquatic plants to a solid sub- 

 stratum is to induce the development of root-hairs, whilst the 

 ventral scales, which are very small and apt to be overlooked in 



"Tui.Rf, 



Fig. 4. — Fegaielln COnica. Transverse section through niidrih of thallus showing the upper 

 zone of air-chambers and the lower zone of compact tissue, with tour of the mucilage 

 sacs. Sm. rh.. smooth-walled root-hairs ; tub. rh., tubarculate root-hairs; v. s., ventral 



scales. X 50. 



the aquatic form, become much larger ; the new branches lose 

 the characteristic strap-like form and are shorter and broader, as 

 in the ordinary terrestrial species of Riccia. 



In Fegatella conica the air-chambers are arranged in a single 

 layer; they are wide but shallow, separated from each other by 

 thin vertical partitions, and roofed over by the single-layered 

 epidermis (Figs. 4-6). All the cells bounding the chambers 

 contain chlorophyll, and those forming the floor grow up into 

 short filaments, each ending in an elongated cell which is 

 produced into a pointed colourless beak (Fig. 5). The compact 

 tissue below the air-chambers is thickest in the midrib ; in the 

 wing on either side it is reduced to four or five layers of cells, 

 gradually thinning out towards the margin of the thallus. In 

 the midrib the compact tissue is traversed longitudinally by 



Natur.ilist, 



