16 BULLETIN 169, U. S. DEPARTMENT OF AGRICULTURE. 



faster at the start. By the time a yellow-pine seedling breaks 

 through the soil cover its root has gone down much farther into the 

 soil than with jack pine at the same age, and the application of a 

 disinfectant to the soil surface at this time is therefore much less 

 likely to injure the yellow-pine root tip. When disinfectants are 

 put on the soil at sowing, the -root tips have not yet emerged from 

 the seed, and yellow pine has no such distinct advantage over jack 

 pine. There is still a difference in depth of planting, however, as 

 yellow-pine seeds are usually covered deeper than those of jack pine 

 and the root tips thus start at a lower level. The more rapid growth 

 is also of some advantage in beds treated before germination, as 

 injury occurs only at times of surface concentration. The root tips 

 of yellow pine may get down far enough to avoid injury from a con- 

 centration which occurs before the tips of jack-pine roots have 

 reached the safety zone. While yellow pine has been less often 

 injured than jack pine by acid applied at the time of sowing, concen- 

 trations occurring while there was a large porportion of yellow-pine 

 root tips in the surface soil have killed large numbers of seedlings. 

 In one extreme case, in which 0.250 ounce of acid per square foot 

 was applied 28 days before sowing and repeated at sowing, with 

 germination following five to six days later, only two-thirds as many 

 seedlings came up as in untreated plats, and of these over 90 per cent 

 died, nearly all as a result of acid injury. On the whole, while 

 yellow pine has been much less often injured by acid treatment, the 

 evidence indicates little, if any, greater resistance of its root tips 

 than that shown by jack pine. 



Corsican pine shows injury in the same way as jack pine (PL I, 

 figs. 2 and 3). It has a seed smaller than yellow pine, but still much 

 larger than jack pine and producing a faster initial root growth. It 

 therefore seems a little less liable to injury than jack pine, for the 

 same reasons that yellow pine is less liable. Norway pine on the 

 other hand, though having a larger seed than jack pine, makes' a 

 much slower initial root growth at this nursery. Its slightly longer 

 germination period gives the acid more time for dissipation, but the 

 indications are that the root tips of this species possess a slightly 

 greater acid endurance than those of jack pine. Corsican and Nor- 

 way pine have not been tested as much as the other two species, and 

 the evidence obtained as to their relative resistance has less value. 



INJURY TO MISCELLANEOUS PLANTS BY SULPHURIC ACID. 



The watering given pine seed beds at the Halsey nursery resulted 

 in the germination of great numbers of previously dormant weed 

 seeds of the species listed on pages 3 and 4. These ordinarily began to 

 appear a little later than the pines and continued to come up in con- 



