Mason — Ligneous Zonation and Die-Back in the Lime, West Indies. 257 



In a word, vegetative activity takes place in the dry months of the year, 

 and the maturation of i'ruit in the -wet. The aridity fluctuates rapidly and 

 markedly in the course of the dry season, while the vegetative meristems are 

 most active. There is generally a bare sufficiency of soil moisture and frequently 

 a pronounced shortage at this season, while the desiccating power of the aerial 

 environment becomes particularly accentuated as a result of the vigour with 

 which the Trade Winds blow about this time. 



The Zonation of the Xylem Cylinder. 



The different types of zonation presented by the Avood of the shoots from 

 the various habitats will be now considei-ed. As the habitats and the condition 

 of the trees supplying the shoots, which are dealt with in this paper, have been 

 recently described by Hardy (2) in the course of his "Studies in AVest Indian 

 Soils," it is possible to consider the zonation in relation to his description, 

 which is reproduced below in italics. The sections, which were prepared by 

 polishing, are enlarged approximately nine diameters. 



The Mulched Plot. — Roseau Lime Experiment Station (fig. 2, Plate XIII). 



Lime trees completely free from die-hack. 



The mulched plot, which supports a vigorous and heaWuj crop of lime trees, 

 is well drained, and is composed of soil in good, tilth and of considerable depth. 

 It is adequately sheltered from winds hy the proximity of lime trees of 

 neighbouring plots, and hy a dense artificial wind-belt that lines the nearest hill- 

 crest. 



Mean Annual Rainfall — 80 inches. 



The environment is on the whole conducive to the maintenance of the water 

 balance of the plant throughout the year, though rather dry periods may occur 

 between February and I\Iay. The presence of the mulch does much, however, 

 to stabilize the soil moisture conditions. 



Xylem Cylinder. 



Growth zones can be distingTiished, though they are not very marked. They 

 are indicated by circumferential areas, in which the large vessels are more 

 densely grouped. Somewhat ill-defined tangentiaUy disposed bands of 

 parenchyma tend to occur ivithin these areas. 



This section does not suggest that the autonomy of the plant was markedly 

 influenced by the adversities of 'the environment. The tendency for the vessels 

 to be grouped is presumably associated with periods of more rapid leaf- 

 production. The parenchyma bands, it is conceived, may indicate intermittent 

 checks in the activity of the cambium as a result of the production of con- 

 siderable tension (1) in the water-tracts of the plant; in other words, they 

 record intermittent periods at which the aridity of the environment (4) became 

 pronounced. 



Olveston Valley, Montserkat (fig. 3, Plate XIII). 



Lime trees free from die-hack. 



The soil in this valley near the sea is typical of the valley soils of the 

 northern part of Montserrat. It is rocky but deep, especially in the pockets 

 between the boulders. The situation is sheltered, and the soil at the time of 

 sampling (April, 1921) ivas moist to the touch.. The iveeds growing between the 

 lime trees were tall and vigorous. 



Mean Annual Rainfall — 60 inches. 



