SEASONAL VARIATION 193 



Cerris, Q. Cocdnea, etc., and other plants, e.g. species of 

 Tamarix, are used to a greater or lesser extent. 



The amount of tannin present in certain plants varies ac- 

 cording to the physiological state, the season of the year, and 

 the conditions of growth. 



In Pinus it is stated that the amount of tannin varies 

 with that of the resin ; thus in the spring it was found that as 

 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 maculatuin 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 im- 

 portance. 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. 



According to the observations of Henri, a calcareous soil 

 is more beneficial with regard to tannin formation than is a 

 siliceous soil. 



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 midtiflortis , 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. pcdunculata. Q. scssilijlora. 



April 14-8 per cent 12-86 per cent 



May 1071 „ 10-46 „ 



June 12-33 .. io"58 .. 



July 9-8 „ 8-II „ 



August .... n-23 „ 10-74 ,, 



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

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



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