J. F. Martlev 267 



Summary. 



1. The character of the double cross-grain of the different Indian 

 woods examined is remarkably uniform and conforms to the following 

 generalisations: 



(a) The grain alternates between right-handed and left-handed in 

 inclination during the growth of the tree, these changes in the inclination 

 being in general synchronous in the trunk at least over lengths of two 

 feet. 



(b) That the grain does not consist of alternate right- and left- 

 handed spirals is due to the rate of change in inclination of the grain 

 not being uniform at any moment during the growth of the tree either 

 in a tangential or longitudinal direction with the result that the double 

 spiral character is obscured, giving place to a serpentine configuration. 



2. Transitional types of grain between straight grain and the full 

 development of double cross-grain are due to variations in the — 



(a) regularity shown in the length of the successive periods. 



(b) regularity in the amplitude of the successive periods, 



(c) stability of the periods over longer or shorter tangential and 



longitudinal distances. 



3. No correlation could be inferred, from the data available, as 

 existing between seasonal changes or periods of growth and the periodicity 

 shown in the inclination of the grain. 



There were indications, how r ever, that both period length and ampli- 

 tude increased with age up to a maximum, and that a long period length 

 was correlated with a big amplitude. Period length responds to the 

 general rate of growth for, in trees of excentric growth, the period length 

 was shortest along the smallest radius. 



4. Fibre measurements in Calophyllum sp. and Chloroxylon Swietenia 

 suggest that a longer fibre length is correlated with inclined grain and 

 a shorter fibre length with straight grain. 



5. The character and widespread occurrence of double cross-grain 

 indicate that it is the expression of some periodic phenomenon whether 

 of internal or external nature, but it remains to be seen to what extent 

 a more extended investigation will bring it into line with other periodic 

 phenomena shown by living organisms. 



This research was carried out in the Woods and Fibres Department 

 of the Imperial College of Science and Technology, South Kensington, 

 while the author was in receipt of a studentship from the Department 

 of Scientific and Industrial Research. 



