260 Scientific Proceedings, Royal Dublin Society. 



yellow clay. The drainage is mainly superficial, the land sloping in the direction 

 of a natural water-course. As a result of a very high rainfall, the soil has been 

 subjected to leaching and washing. 



It is markedly acidic in reaction fpH 4'/), and is almost continuously water- 

 logged. 



Mean Annual Rainfall — ^200 inches. 



Xylem Cylinder. 

 The zonation here is essentially similar to that in the former section. The 

 growth of the cambium has evidently received repeated checks. The conductivity 

 of the wood is small. The soil in which the trees were rooted was indubitably 

 physiologically dry for the greater part of the year as a result of a low oxygen- 

 supplying power, and, possibly, the presence of toxic substances, and not, of 

 course, from an excess of soluble salts. It is probable that the numerous 

 irregularly distributed parenchyma bands are due to the dxying blast of the 

 Trade Winds. 



O'Gaera's Coastal Region, Montserrat (fig. 9, Plate XVI.) 



Lime trees exhibiting die-bach. 



This locality is situated on loiv ground near the extremity of a steep tahis 

 slope. The soil is someivliat shallow and stony, with 'pockets between the rocks. 

 It was dry and compacted at the time of sampling (April, 1921), and its weed 

 flora was withered. Under drainage appears not to be good, for the presence of 

 nut grass (Cyperus rotundus) and Commelina nudiiiora, growing amongst the 

 xerophytic short-lived annuals that make the natural plant association, iiidicates 

 that the land is subjected to periodic water-logging. 



Mean Annual Rainfall — 43 inches. 



Xylem Cylinder. 



There is here a very marked differentiation into zones simulating "spring" 

 and "autumn" wood. It will be observed how very sharply these zones are 

 delimited from one another. It will be evident that the rate of growth must 

 have been checked with great rapidity. This is possibly the result of the periodic 

 water-logging to which Hardy refers. 



Conclusions. 



The interpretation of the zonation exliibited by the woody cylinder of the 

 shoot of an arborescent evergreen, particularly in a tropical climate, is evidently 

 a task beset witli no little hazard. As yet, it would seem, the i^roblem has never 

 been approached experimentally. It is but natural that this should be so, for 

 the prosecution of work of this nature would call for resources and equipment 

 at present possessed b.y no tropical, and few northern, botanical departments. 



It has been generally assumed by paleontologists that rings of growth in the 

 stems of fossil plants indicate the existence of a Temperate Zone climate and 

 their aljseiice a more ec[uable one. In the woody cylinder of the shoot from 

 the Lime Experiment Station of Dominica, where the moisture conditions are 

 more generally favourable for growth than in any of the other habitats visited in 

 the course of this survey, zonation is scarcely appreciable. It is indicated 

 merely by circumferential areas, where the large vessels are somewhat more 

 densely distributed than elsewhere, and within which ill-defined tangential bands 

 of parenchyma occur'. This grouping of the vessels, which culminates in some 



