J. F. Martley 265 



two heads. Under "Induced Periodicity" are included all those cases 

 which show a more or less direct correlation with the rhythm in external 

 conditions; for instance diurnal and seasonal changes are reflected in the 

 periodicity shown by growth and leaf-fall. 



Under "Innate Periodicity" are included all those cases in which 

 no correlation can be demonstrated to exist between the rhythm shown 

 by a living object and the rhythm in external conditions, examples being 

 the alternating streaming movements of the protoplasm of Mvxomycetes 

 and the leaf-fall of trees of tropical climates which are characterised by, 

 at the most, only feebly marked seasonal changes (Schimper(4)). 



It is under this latter head that the phenomenon of double cross-grain 

 naturally falls for, relying on the evidence of the rings, no correlation 

 could be established between seasonal changes and the period of the 

 grain. 



Some interesting analogies are shown between double cross-grain 

 and the leaf-fall of trees native of regions showing absence of seasonal 

 changes (see Schimper). Corresponding with the full development of 

 double cross-grain are those trees which completely shed their foliage 

 at regular intervals varying from two to twelve months, irrespective of 

 the time of year. Trees in which the periodicity of the cross-grain is 

 synchronous only within narrow limits in the trunk are paraUeled by 

 those trees which, considered as a whole, are evergreen, but in which the 

 individual twigs are alternately bare and clothed with foliage. 



If this type of grain is the expression of some periodicity in the life 

 processes, it is to be expected that other periodic variations, synchronous 

 with the variations in the inclination of the grain should be found. With 

 this object in view the fibre lengths in Chloroxylon Swietenia and in 

 Calophyllum were determined along a stick at points where the grain 

 was straight and where it was inclined at a maximum. 



The figures which are shown in Table VIII are very suggestive, but 

 the inference that there is a correlation between a longer fibre length 

 and inclined grain has no very sound statistical basis for 500 is not a 

 large enough basis for determining a mean where the deviation from the 

 mean is so large in comparison to the difference in the mean fibre length 

 of the successive samples. 



Since very little is known of the mechanical effects due to the increase 

 in length of the young fibres it is impossible to say whether the changes 

 in the inclination of the grain might be directly attributable to a variation 

 in fibre length such as is indicated above. The impression obtained, 

 how r ever, during the course of the investigation was that the changes in 



