CHORUARIACE^. 45 



the structure of Ectocarpace.e, but allied in their fructifica- 

 tion too strongly to Leathesia to be separated from that ge- 

 nus. The spoj-es in this order are very generally obovate, 

 tapering to their lower extremity and very obtuse above, al- 

 ways furnished with a pellucid perispore, and containing a 

 dark-coloured homogeneous mass. They are attached to the 

 sides of the filaments composing the periphery or outer stra- 

 tum of the frond, and very generally are surrounded by pa- 

 ranemata. In Ralfsia alone they form prominent wart-like 

 sori, similar to those of Dictyotace/E. The prevalent colour 

 of the frond is olivaceous, varying from a dark brown to a 

 light greenish olive, nor is it much changed by drying. 



In this order we have an obvious declension from the 

 structure of the more perfect Melanosperms ; as it were, the 

 resolution of a compound frond into its constituent parts. In 

 the Fucaceic, the highest plants in the series, the frond is si- 

 milarly constructed of interlacing filaments; but in that order 

 the filaments are so closely pressed together and compacted 

 into a fleshy substance, that they cease to be obvious except 

 after a minute dissection. But in the ChordariacecB the 

 sti'ucture is so loose that the filamentous nature of the frond 

 is apparent the moment that a branch is brought under a 

 moderate magnifying power. 



The plants comprised in this order, notwithstanding a 

 considerable difference in habit, form a natural group allied 

 through Ralfsia to the Dictyotace^, and through Elachis- 

 tea to the Ectocarpace^. There are collateral affinities 

 also with GioioclacUeoi and Batrachospermace^, whose 

 fronds have a similar structure. 



The Chordariace^ are widely dispersed ; the genera 

 Mesogloia, and Chordaria, and perhaps some others, cosmo- 

 politan. Leathesia tuheriformis is as common on the shores 

 of South Africa as on those of Britain ; and so is Chordaria 

 flagelliformis . 



SYNOPSIS OF THE BRITISH GENERA. 



* Frond cylitidrical, branching. 



I. Chordaria, Axis cartilaginous, dense ; filaments of 



the circumference unbranched. [Plate 10, A.] 



II. Mesogloia. Axis gelatinous, loose ; filaments of the 



circumference branching. [Plate 10, B.] 



