THE RESERVE MATERIALS OF PLANTS. 69 



The view that these bodies have a nutritive value has 

 been supported with some emphasis by other writers. 

 Wigand associated it very closely with the carbohydrates, 

 and thought it was an essential factor in vegetable meta- 

 bolism. Wiesner also supported the view of its carbohy- 

 drate relationships, and indicated a probability that it stands 

 between the starch and cellulose groups and the great class 

 of resins, etc. The latter relationship has been again 

 brought forward by Hillhouse (70), who found in Pinus 

 sylvestris that as resin increases in the stem tannin dimin- 

 ishes in like proportion, and that the cells surrounding the 

 resin ducts invariably show its presence. Hartig suggests 

 that tannin remains in the oak through the winter in the 

 form of grains similar to starch grains, but distinguishable 

 from the latter by characteristic reactions. These grains, 

 he says, are dissolved and utilised in the spring. In his 

 later writings Sachs inclines to the same view ; he says 

 that besides those which must be looked upon as excreta or 

 bye-products, some of the tannins of the oak are most likely 

 to be regarded as reserve products, on account of their origin 

 and disappearance and their behaviour generally during the 

 growth of the plant (71). 



The localisation of tannin in the different parts of the 

 plant does not give us much assistance in determining which 

 of these views has most to support it. It is often found in 

 special sacs in the midst of metabolic tissues ; it is very 

 frequently found in epidermal cells, either in the interior or 

 saturating the cell wall ; it is extremely prominent in bark. 

 These positions certainly suggest that it is of but little value 

 as a food-stuff; on the other hand it is often abundant in 

 assimilating parenchyma in which starch formation is pro- 

 ceeding. 



In Hillhouse's paper (70) already alluded to, the author 

 describes a considerable number of observations he made to 

 determine whether or no a disappearance or diminution of 

 tannin could be detected in the spring, and if so, whether it 

 was a reasonable conclusion that such diminution indicated 

 a utilisation of the vanished portion. 



He investigated a large number of trees in which tannin 



