J. F. Martlky 229 



defined by one or more of the following structural characters (see 

 (J room (2)). 



(1) Variation in the size of the vessels (Oak, Ash). 



(2) Variation in the distribution of the vessels (Apple, Hawthorn). 



(3) Decrease in the radial dimensions of one or more layers of wood 



elements (Sycamore, Poplar). 



(4) Local decrease in the radial dimensions of the ray cells (Oak, 



Poplar). 



(5) Local broadening of the rays (Oak, Beech). 



(6) Presence of a more or less continuous sheet of parenchyma 



(Poplar). 



(7) One or more layers of cells with darker contents. 



Where the size and distribution of the vessels is uniform or nearly so 

 and the remaining characters are ill-defined, it is often difficult to recog- 

 nise a structural limit to the ring under the microscope, although rings 

 can be recognised by the naked eye. This is the case with Boxwood and, 

 to a lesser extent, with Pearwood. 



Experience has shown that these rings are annual and are correlated 

 with leaf fall and cessation of active growth before the cold weather 

 sets in, and with the production of fresh foliage when conditions are 

 again suitable for the assumption of growth in spring time. 



All the Indian timbers examined in the course of this investigation 

 showed concentric rings which, to the eye, were as well defined as those 

 of many temperate climate trees. 



In none of the species examined by the detailed method did the size 

 or distribution of the vessels play any part in the definition of these 

 rings, thus resembling the Willows, Poplars, and Horse Chestnut of 

 this country. 



The structural definition of the rings of these species, based on a 

 limited number of sections, was as follows: 



In Chloroxylon Swietenia the rings were very clearly defined by a 

 layer or sheet of parenchyma two or three cells deep characterised by 

 numerous simple pits. 



In Shorea robusta the rings were defined by a sheet of parenchyma 

 three or four cells deep. A slight tangential broadening of the rays was 

 apparent where they passed through this sheet. Cysts or canals, probably 

 of schizogenous origin, were of frequent occurrence in this layer. 



The ring in Hardwickia binata was defined by a layer, three to six 

 cells thick, consisting of parenchyma and of elongated narrow-lumened 



