262 Scientific Proceedings^ Royal Dublin Society. 



with tlie actual distribution of Lime cultivation in the West Indies. That the 

 tree can thrive under a wide range o£ relatively static edaphie conditions 

 (hydrogen ion concentration, etc.) has been convincingly shown by Hardy (2). 

 There can be little doubt that the rate, rather than the amount or duration of 

 desiccation is in many cases of extreme importance in determining the distri- 

 bution of plants. It is possible that this is one reason why certain plants will 

 grow vigorously in clay soils and fail completely where the colloid content is 

 small. 



In conclusion, the writer wishes to express his indebtedness to Mr. Robson, 

 in Montserrat, and Mr. Keys, in Dominica, for making observations on the 

 l^eriodicity in the growth of the Lime tree. 



Summary. 



1. In this paper the results of an examination of the ligneous zonation of a 

 number of Lime shoots from trees growing in different paxts of the West Indian 

 islands of Dominica and Montserrat are considered. Half of the shoots were 

 collected from trees affected with die-back. 



2. The zonation in the woody cylinders from healthy trees indicates a rather 

 definite periodicity in the activity of the cambium. Tangential bands of 

 parench^ana are generally distributed within the more porous zone of vessels. 



3. Inasmuch as the Lime tree in these islands makes its vegetative growth 

 during the dry season, it was inferred that the zones of vessels registered the 

 production of leaves at this period, while the water-supply was adequate, and 

 that the tangential parenchyma which is distributed Avithin these zones originated 

 at periods of relatively great aridity. Rapid fluctuations in the aridity of the 

 environment, which the association of the porous vessels and the circumferential 

 parenchyma indicates, are characteristic of the climate in the dry season. 



4. The wood of shoots from, trees affected with die-back exliibited considerable 

 irregularity in the distribution of the parenchyma bands. All the sections 

 suggested that the cambium had been exposed to sudden cheeks in its activity. 



5. It was tentatiA'^ely concluded that an important factor in causing the dying 

 back of the shoots was rapid and repeated desiccation of the meristems. In the 

 terminal meristem this resulted in a premature loss of the dominance of the 

 apical bud, and its replacement by daughter shoots, which in turn suffered the 

 same fate; and in the cambium by the production of tangential parenchjona. 



LITERATURE CITED. 



1. Dixon, H. H., 1914. — Transpiration and the Ascent of Sap in Plants. 



London. 



2. Hardy, F., 1922.— Studies in West Indian Soils. West Indian Bui. xiv, 2, 



189-213. 



3. Jeffrey, E. C, 1917.— The Anatomy of Woody Plants. Chicago. 



4. Livingston, B. E., and Hawkins, I. A., 1915. — The Water Relation between 



Plant and Soil. Carnegie Inst, of Washington, Pub. 204. 



5. Livingston, B. E., and Koketsu, R., 1920. — The Water-Supplying Power of 



the Soil as related to the Wilting of Plants. Soil Science,' 9, 469-485. 



6. Mason, T. C, 1921.— The Water Balance of the Plant and its Sigiiiiicanee in 



Crop Production. West Indian Bui. xviii, 4, 157-184. 



7. Mason, T. G., 1922.— The Physiological Humidity of the Soil and its Direc* 



Determination. West Indian Bui. xix, 2, 137-155, 

 S. Nowell, W. — [In the Press.] 



