TAXONOMIC VALUE OF GROWTH-FORMS. 271 
are long and the horizontal layer is thickened, in No. 9 the stems are very short and there 
is no abnormal thickening whatever. 
As an illustration of another kind, take the calicles shown on figs. 8 and 9, on Pl. XXVIII. 
The former are of the remarkable cluster of tall, tapering spikes from the Java Sea (No. 2); the 
latter, with thin, minute, insignificant ragged skeletons, are of the Christmas Islands (No. 1), 
with reference to which Dr. Andrews informs me that it appeared to be quite amorphous, 
forming patches of no definite shapes all over the reef, At the first glance at the figures we 
seem to understand how such calicles might be referable to such growth-forms ; but the reasons 
have to be discussed, and that will only be when we have many such cases at our disposal for 
comparison. 
Need I again enforce the argument that, in the presence of these uncertainties as to the 
taxonomic value of the principal characters of growth-form and calicle structure, and of our 
ignorance as to how far variations in the one influence variations in the other, all attempts at 
a specific classification are premature? The only natural classification at present possible is a 
tabulation of the ascertainable facts. 
A comparison of the branching forms of the West Indies where they appear to be in a 
great majority and strikingly uniform, with those of this Indo-Pacific area, which our lists 
show to be in a decided minority and very variable, can hardly fail to be of great interest. 
At present we have no information as to the causes of this contrast in the relative propor- 
tions of the two kinds in the two regions. On the lists above given we may call attention 
to the relatively large number of branching forms from North Australia and to their 
absence from the Great Barrier Reef. 
