37 
In wet places oak ties often become water-soaked and will sink when 
thrown into the water. 
Change of sap /rood to heart-wood, — The sap-wood of the White Oak 
changes to heart-wood in ten to fifteen years, much earlier than that 
of some of the other oaks. This is a valuable feature, as ties are cut 
mostly from small timber of the proper size and flattened on two sides, 
leaving the sap-wood on the remaining sides. In many cases the bark 
is not removed, but it should be at the time of felling the tree, espec- 
ially if the temperature be about 50° or G0° F. If the wood is cut 
daring active growth the sap furnishes a good medium for the growth 
of various ferments, which, if special care is not taken to prevent 
their growth, will affect the sap-wood and eventually the heart- wood. 
When such fermentation has taken place and is afterward checked 
by drying, the wood is discolored and is called " dozy," and will rot 
quickly when placed in the road-bed subject to conditions of warmth 
and moisture. 
Note. — The controversy as to the influence of the time of felling on the durability 
of tho wood cannot yet be said to be definitely closed. The most recent investiga- 
tions under this head, published by Professors Hartig, Polcck, and Dr. Lehmanu, 
would indicate that the question cannot bo answered generally, but that the answer 
is dependent on different conditions in each special case. 
Tho "dry-rot" fungus (McraUus lacrymans, Schum.) being found to be the principal 
destroyer of the wood used in building, Professor Polcck was induced to examine the 
mineral constituents of timber felled in the winter and in the summer with regard 
to the requirements of this fungus, and was led to state that the summer-felled tim- 
ber affords a better supply of nourishment to the fungus than that felled in winter, 
the former being five times as rich in potash and eight times as rich in phosphoric 
acid as the latter. The cxj>eriments which confirm this view were conducted with 
blocks of timber inclosed in casks. Unfortunately, later on, Professor Poleck discov- 
ered that the timber procured for him, purporting to be winter- felled wood, was in 
reality raft-timber; and he has ascertained that timber which has been immersed in 
water is no longer liable to tho attacks of " dry-rot," the effect of the water being to 
dissolve out slowly the albumen and salts, thus depriving the fungus of the neces- 
sary nutriment for its development. So much so is this the case that in Alsace it is 
customary to specify that only raft-timber shall be employed. 
In opposition to the theory of Professor Poleck a number of experiments were car- 
ried on by Professor Hartig. In the first place he shows that at tho end of April the 
sap has not risen in the timber, and that no mineral matter can have been stored up 
in the wood-cells which were not present at the beginning of the winter, and that 
the true summer-felled timber must, if anything, be poorer in mineral salts than that 
felled in the winter. His analyses confirm this view, showing 8.42 per cent, of phos- 
phoric acid in winter wood as opposed to 5.80 per cent, in summer-felled wood; and 
while Professor Poleck insists upon the necessity of phosphoric acid for the growth 
of tho fungus, Professor Hartig lays most stress upon tho presence of ammonia or 
potash salts as being essential. 
Professor Hartig's experiments made with pine and fir, felled for the purpose and 
stored in a specially constructed cellar, are most elaborate and minute, the general 
result being that both summer- and winter-felled damp fir and pine (two kinds of 
woods behaved alike) lost equally in weight. When, however, dry winter wood was 
contrasted with wet winter wood, the results were astonishingly different. In the 
case of fir the dry wood lost 11 per cent, in weight, while the wet wood lost 23.1 per 
