11 MUSCINEJE—HEPATICM—MARCHANTIALES 43 



in two rows. Leitgeb ((7), iv., p. 17), recognises two types 

 of these organs. In their earHest stages they are aHke, and 

 both arise from papillae close to the growing point. In both 

 cases this papilla. is cut off from a basal cell, but in the first 

 type {Sauteria, Targionia, Dumortiera) it remains terminal, 

 usually forming the tip of a leaf-like terminal appendage of 

 the scale. In the second type, represented by most of the 

 other genera, this originally terminal papilla is forced to one 

 side by the development of a lateral appendage to the scale, 

 which, arising at first from a single cell, rapidly increases in 



Fig, II. — Fimbriaria Californica. Development of the pores upon the archegonial 

 receptacle, X260. A, B, C, in longitudinal section; D, view from above. 



size, and forms the overlapping dark purple marginal part of 

 the scale so conspicuous in many species. 



In different parts of the thallus are found large mucilage 

 cells, which are usually isolated ; or in Conocephalus, according 

 to Goebel's (i) investigations, and those of Cavers (6), they 

 may form rows of cells which become confluent so as to form 

 mucilage ducts. In the earlier stages these cells have walls 

 not differing from those of the adjacent cells, but as they grow 

 older the whole cell wall is dissolved, and the space occupied 

 by the row of young cells becomes an elongated cavity filled 

 with apparently structureless mucilage. These cells are recog- 

 nisable at an early period, as their contents are much denser 

 and more finely granular than those of the adjacent cells. 



