SEASONAL VARIATION 



269 



the tannin decreased in amount so the resin increased. Pea- 

 cock * found that in Heuchera americana the tannin was most 

 abundant in October and least in May, whilst the amount of 

 starch present was greatest in March. Trimble and Peacock 

 found that in Geranium maculatum the maximum amount of 

 tannin obtained in April, i.e. just before the period of flowering. 

 From this phase onwards there was a gradual decrease until 

 the minimum was reached in October. 



It is found that the more vigorous trees yield the most 

 tannin, and that the character of the soil appears to be of 

 importance. It has been found that oak trees grown in a poor 

 dry soil yield a bark richer in tannin than those grown on the 

 soil of damp lowlands. 



It is not impossible that the different yields of tannin 

 given by the same plant grown in different situations may be 

 due to the relative abundance of the mineral food-materials ; 

 thus it has been found that in some instances, e.g. in Spirogyra 

 and Phaseolus multifiorus , the formation of tannin is inhibited 

 by the absence of chlorine. 



With regard to seasonal variation in the amount of tannin 

 in the bark of the oak, the following estimations are given by 

 Eitner : — f 



Q. pedunculata. 

 April . . . 148 per cent. 



May .... 10-71 



12-33 .. 

 9-8 

 11-23 .. 



June 



July 



August 



Q. sessiliflora. 

 12-86 per cent. 

 10-46 

 10-58 

 8-11 

 10-74 „ 



For the inner bark of the American oak, Quercus Prinus, 

 Trimble J found the following seasonal variation : — 



As a general rule the barks collected in May and June are 

 the richest in tannin, but this does not hold for all parts of 



* Peacock : " Amor. Journ. Pharm.," 1891, 172. 



t Eitner : " Der Gerber, Vienna," 1878, 4. 



} Trimble : " The Tannins," Philadelphia. 1892. 1894. 



