526 DR. F. W. JONES ON GROWTH-FORMS [Juue 18, 



that is abundant in tlie islitnd.s, and it grades very naturally into 

 the plate-like growths on the one hand, and into the complicated 

 branching forms on the other. 



In theinan}' highly branched forms of vegetative growth, the 

 growing cells form a cluster, and this cluster divides as it grows 

 upwards, with the development of many growing points at 

 intervals on the pa-rent stem. The cluster may be of various 

 shapes, and its form determines that of the stem that results 

 from it. The stem may be rounded or flattened, may be thin or 

 thick, and it may bi'anch at frequent intervals, or it may scarcely 

 branch at all, so that straight rods of unifoi'm thickness may be 

 characteristic of the vegetative growth of the coral. 



Another modification of this method of growth is that in which 

 practically the whole colony represents the growing point, and 

 then the entire mass grows upwards as a solid column ; or the 

 growing point may be confused and irregularly distribvited, and 

 then an irregular, lumpy amorphous mass results. 



Whatever"^ the vegetative growth may be, it is m these cases 

 the product of a mass of growing cells, and these cells are being 

 pei'petually renewed, so that the growing point always contains 

 the youngest cells in the colony. 



In Gh'otqi 2, however, this state of things is entirely altered, 

 for there one zooid, which is situated at the extremit}^ of the 

 stem, and which I shall call throughout the "dominant apical 

 zooid," constitutes the growing point ; and this zooid is the parent 

 of the entire colony. 



The zooid that settles down to establish a Madrepore colony has 

 the peculiar innate property of perpetual growth and perpetual 

 youth ; and this original zooid grows up and up, budding new 

 zooids from its sides, until destruction overtakes it. As a, matter- 

 of fact, a Madrepore colony usually starts as a flat growth which 

 spreads from its edges, but this method of growth lasts for only 

 a veiy short time ; and all the characteiistics of the " dominant 

 zooid" — which is here the cential zooid — are even then well 

 marked. 



Besides possessing these peculiar jjhysiological distinctions, the 

 "dominant zooid" is marked off from its fellows by a great 

 anatomical feature, for it is a symmetrical zooid. Of the many 

 thousands of daughter zooids budded ofi' from the " dominant 

 zooid," all are not alike ; the great bulk are asymmetrical, and are 

 but little raised from the general surface of the coral, but here 

 and there a prominent and symmetrical zooid is given oflf. Like 

 the " dominant zooid," these lateral zooids possess the power of 

 perpetual gi'owth, and they are the agents in forming the latei'al 

 branches. Under certain conditions only very few of these 

 prominent lateral zooids are produced, and then the resulting 

 veo-etative growth consists of long straight stems with but few 

 side-branches. 



The typical form of vegetative growth of the Madrepores is 

 therefore a branching system, but many variants of this form are 



