SUMMARY.1The 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 lefthanded 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.2Transitional 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.3No 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, however, that both period length and amplitude 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.4Fibre measurements inCalophyllumsp. andChloroxylon Swieteniasuggest that a longer fibre length is correlated with inclined grain and a shorter fibre length with straight grain.5The 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 Scientitic and Industrial Research.In conclusion I wish to record my thanks to Professor Percy Groom for suggesting this investigation, providing the material and for help throughout t