RHODOSPERME®. 19] 
The genus Ceramiwm comprises several well characterised species, 
several of which occasionally present varieties of form or structure which 
are more or less puzzling to the uninitiated. However, there are at least 
eleven British species which are now generally acknowledged, and as 
they represent the three sections into which this group was divided by 
Dr. Harvey, I shall describe them according to that characteristic arrange- 
ment. 
The first section, Rubra, contains the well-known Ceramium rubrum 
and its varieties. So widely dispersed is this common-species, that Dr. 
Harvey says, “it is met with almost wherever marine plants will grow, 
from high arctic to high antarctic latitudes.’’ On our own shores this 
Fie. 176. Ceramium rubrum, with favelle, magnified. 
plant assumes such a variety of forms (according to the nature of the 
locality or the depth of water in which it grows), as frequently to puzzle 
experienced botanists as well as young collectors of alge; however, 
well-grown specimens, and particularly those which are in fruit, are 
easily recognized. Fig. 176 represents a branch of one of the forms 
of Ceramium rubrum slightly magnified, bearing involucrate favelle. 
Although, like all the plants of this group, whose stems and branches, 
are regularly more or less chequered by alternate dark-coloured nodes 
or joints, and colourless dissepiments or inter-spaces, the nodes and 
dissepiments of Ceramiwm rubrum, and its varieties, are more or less 
eoated with coloured cells, hence the name of the typical species. The 
