1906.] Forestry at Nuknberg Exhibition. 



341 



most, definite information as to the rate of destruction can be 

 obtained. 



A number of cross-sections exhibit the inexpHcable con- 

 dition of things that growth is more rapid on the underside than 

 on the upper side of the branch of a conifer, whereas in the 

 branch of a dicotyledon the opposite is the case. This may be 

 seen by cutting off horizontal branches of the two classes of 

 trees named. In the case of the conifer, the pith will be found 

 to be nearer the upper than the lower side of the section, while 

 in the dicotyledon the shortest radius is on the under side. The 

 horizontally disposed roots of trees (the spruce is a good 

 example) also show marked eccentric growth, but in their case 

 the character of the eccentricity is always the same, the greatest 

 growth, and therefore the longest radius, being on the upper 

 side. It is evident that the upper side of a root is subjected to 

 less pressure from the soil than the lower side, and as the 

 cambium makes most wood where the pressure is least, the 

 greatest growth is found in a root precisely where it is to be 

 expected. But the variable condition of things in the branches 

 of conifers and dicotyledons has always been a puzzle to 

 botanists, and no satisfactory explanation is yet available. 

 Nor is it quite easy to say why, in a tree grown on a steep 

 hillside, greater growth should be shown on the side away from 

 the hill. 



A fine series of young trees has been prepared to illustrate 

 the fact that most of the roots of forest trees live in intimate 

 association with delicate fungus mycelia {uiycorhiza). This 

 relationship has not been fully worked out, but it is evident that 

 it is of the same character as the symbiosis that exists between 

 the roots of leguminous farm and garden crops and bacteria. 

 Sometimes the mycelia work their way between the cells of the 

 epidermis and cortex (e.g., Scots pine, spruce, beech, oak, birch), 

 and roots so affected are called ectotropic mycorJiiza. In other 

 cases the fungus strands actually penetrate the cells of the root 

 {eitdotropzc ///j^r^T/^/^cz), examples of which are TJiiija occidoitalis 

 and Yew. 



In Bavaria, as in this country, oak bark has experienced a 

 great drop in price during the past twenty years, the price per 

 cwt. having fallen from 4s. Qd. in 1885 to is. pd. in 1905. Con- 



