270 MADREPORARIA, 
OBSERVATIONS ON THE TAXONOMIC VALUE OF THE GROWTH-ForRMS IN PORITES, AND ON THE 
RELATIONSHIP BETWEEN GROWTH-FORM AND CALICLE STRUCTURE. 
There is a natural tendency, in the presence of so much variability, to assume that the 
growth-form is for all practical purposes a factor of the environment alone. This is, however, 
only occasionally the fact. There is abundance of evidence to show that each kind of Porites 
has its own principle of growth, which, in a neutral or unchanging environment, would always 
repeat itself. In Montipora it is known, for instance, that small areas of the sea bottom may 
be covered with some strange but constant form.* Then, again, forms of Porites which are 
accidentally overturned mostly show a tendency to repeat the same shape of stock upon the 
prostrate previous growth. Further, branches or columns, which spring up from one and the 
same explanate growth, all have the same character. All these show that there is a principle of 
growth belonging to each different kind of calicle. But, as against this, we recall the evidences 
already given of the power of the environment to reduce specimens of different kinds of 
corals, not only of one and the same genus, but even of different genera, to the same forms. 
Compare the facts, that from the Amirantes we have Montipore and Porites found side by 
side, so alike that only an expert can distinguish them, and again in the China Sea we have 
Porites and Goniopore showing in the same locality the same remarkable specialisations of the 
calicle skeleton.t 
Every specimen, then, which we examine has to be looked at as the result of these two 
factors. Guessing as to which has played the chief part in its production is useless; we have 
only the path of patient research before us. The lists given above, which are necessarily 
provisional, are to be regarded as an attempt at a systematic arrangement of the data, to be 
corrected and added to as new facts eome to light. 
We may, indeed, at once gather from these lists that while in some forms the growth 
natural to them in a neutral environment will be very difficult to find out, owing to the 
excessive plasticity of the colony, a number of forms (e.g. P. Ceylon 4) will be found, the 
growths of which show a marked tendency to repeat certain form-features. We may hope, 
therefore, that in time we shall be able to discover in such forms some correlation between 
calicle and growth-form. 
We may call attention to the following cases. In branching forms there is a tendency in 
the interests of strength to thicken the horizontal (or in the section of a stem the concentric) 
layers of the calicle skeleton. The thickening may take place high up in the skeleton, making 
all the skeletal elements at the surface more or less flaky (see the cases marked a in list G, a, 
above). It may take place at varying depths of the calicle, consequently allowing the 
trabecule to appear at the surface as the most conspicuous elements (see cases marked # in 
the same list). Lastly, the whole of the skeleton may be equally thickened. The cases of 
P. Tonga Islands 8 and 9 are interesting ; they are clearly related, but in the former the stems 
* Cf. “The Naturalist in Australia,” by W. Saville-Kent, 1897, p. 146. 
t See P. Amirantes 3, p. 225. 
t See P. China Sea 4, p. 168. 
