GEOLOGICAL HISTORY OF THE CHAROPHYTA. 79 



types and condition of preservation, represent by far 

 the most productive field for the study of the fossil 

 forms of this group which has yet been discovered. 

 The remains occur in limestone and chert and comprise 

 both vegetative parts and fruits, the latter being in a 

 few cases attached to the branchlets. The prevalent 

 type, described and figured by Clement Eeid and myself 

 under the name of Clavator (16), is the only one which 

 has yet been worked out. Some sections of the stem 

 were described and figured by Mx. B. B. Wethered in 

 1 889 (28). Whether or not it was the Chara Purbeckensis , 

 of Forbes MS., there is no evidence to show. Clavator 

 presents some very remarkable points of difference from 

 any other Charophj'-te, recent or fossil. Its outstanding 

 features are : 



1. The oogonium being enclosed in an outer utricle, 

 or nut (see Plate XLV, Fig. 8). These utricles have longi- 

 tudinal ribs with somewhat rounded hollows between, 

 and our conclusion was that the ridges represent part 

 of the side walls of more or less cylindrical cells adnate 

 to one another, and of which the outer portions of the 

 walls had not been preserved. In a living South African 

 species of Chara the bracteoles and bract-cells which 

 partially surround the fruit are swollen in the middle 

 and taper at each end, the tips tending to converge. 

 Were these to become more numerous, and adnate to 

 one another, a structure would be produced very similar 

 to the utricle of the Purbeck plant as we interpreted it. 



2. The remarkable development of the cortex of the 

 stem. The stem-cortex consists invariably of twelve 

 rows of cells. On the portions of the stem remote from 

 the nodes the twelve rows are of about equal diameter 

 (see Fig. 2) ; as they approach a stem-node six of them 

 rapidly increase in diameter (see Figs. 3-4), so that at the 

 node they form a spindle-shaped thickening, in most 

 cases tapering about equally upwards and downwards 

 (see Fig. 1). The alternating six rows do not increase 

 in size, but are forced outwards by the larger ones, and 

 lie in valleys between them (see transverse section,. 



