FOREST COMMISSIONER S REPORT. 93 



which occasionally bore holes into it. This injury is not very 

 widespread, however, and is rendered less serious from the 

 fact that it is usually confined to the upper part of nearly ma- 

 ture trees. Old trees are seldom injured by frost or drought. 

 Young sprouts, especially those which start in midsummer, may 

 be killed back by early fall frosts, liut only the tips are injured, 

 and the plants seldom killed. The collection of birch bark for 

 cups, baskets, and other fancy and ornamental articles is respon- 

 sible for the death of many trees. Careless collectors frequently 

 girdle trees in the neighborhood of summer resorts, and many 

 dead trees can l)e found standing as a memorial to their work.. 

 A little care in taking only small sections of the outer bark 

 might ])revent niucli of this injury. 



KEPRODUCnON. 



By Seed. 



Paper l)irch is a prolific seeder. There are no tlefinite seed 

 years as with many cither species, and a considerable amount of 

 seed is borne each year. Individual trees may not bear equally 

 heavy crops year after year, but when one has a light crop, 

 another may have a good one, so that the amount of seed pro- 

 duced annually is fairly constant. The germinating per cent 

 is not verv high. A sample count showed the fertility by in- 

 spection to be 68 per cent. A germination test, even in the 

 greenhouse, would probably give a much lower figure than this, 

 and under natural conditions the proportion of seeds which 

 succeed in germinating would undoubtedly be still further re- 

 duced. The best seed is produced in greatest amount by full- 

 crowned trees similar to those found in the open. 



The seeds are very light. A sample count of seeds collected 

 in Maine in 1905 showed that there are more than 38,000 seeds 

 to one ounce. This lightness coupled with their wings enables 

 them to be carried readily to great distances by the wind. This 

 accounts for the exceedingly wide distribution of the birch and 

 for its sudden appearance in dense stands on burned or cut- 

 over areas even when there is not a single seed tree in the imme- 

 diate vicinity. The seeds are not, as is sometimes mistakenly 

 assumed, already in the ground, but are blown in by the wind, 

 which is by far the most important factor in their distribution. 



The best germinating bed is a bare mineral soil. A heavy 

 ground cover of leaves, fluff, sod, or other material checks the 



