i:;2 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



An indication of the limits of error of the above method may 

 be obtained from the following : — " The inaccuracies of the 

 photochemical method of measuring light-intensity are not 

 great. Ordinarily the error does not amount to more than 

 ID per cent., and by repeated measurements it can be reduced 

 to 5, and even to 2-5 per cent.''^ 



Results. 

 Oak — Observations in Eleven Groups (Fig. i). 



Beech — Observations in Ten Groups (Fig. 2). 



Grai>hic Rkpkksentation. 



The number of .seedlings per -8 square pole for the species 

 Vjeech and oak is plotted vertically, while the specific photic 



' .See J.ii(ht in Kelalion lo 7'n:<; Grozvlli, by Raphael Zon and Henry S. 

 Graves, U..S. Department of Aj^riculture, J'orest Service — Bulletin 92. 



