2011年英语四级阅读备考材料（17）_第2页

Developing a White Pine Strain Resistant to Blister Rust. You can always identify the white pines because the needles are in clusters of five—and there are five letters in the word w-h-i-t-e. This also applies to the sugar pine of California, which is also a white pine. Count the letters in s-u-g-a-r. Five again!

　　White pines have a particularly vicious enemy—the disease called blister rust. Long ago scientists found that the disease spores do not go from one white pine to another; they need an alternate host, either currant or gooseberry bushes. Destroy these bushes near white pine trees and the disease is stopped. This sounds easy, but it is a very expensive and tedious job.

　　Well, foresters aren't satisfied with that. They have found a few—just a few—white pine trees that are resistant to the disease. Starting with these few trees, the Forest Service and other public agencies in the United States and Canada are trying to develop a resistant strain of white pine that will still have good timber quality.

　　How to nail a House Together. Nails are the principal fasteners used in building a wood-frame house. How these nails are selected and used determines how solid the building will be. It's important to know the size, number, and placement of nails necessary to construct a house so it will successfully resist such forces of nature as strong winds, hurricanes, earthquakes.

　　The Forest Products Laboratory at Madison, Wisconsin, a unit of the Forest Service, has made exhaustive studies of nailing techniques. The results, contained in a booklet, Technique of Hose Nailing, are of value to engineers, architects, carpenters, and home-owners as a guide to the building of better houses. With the booklet (available from the U. S. Forest Service) one can judge the quality of the nailing in the construction of his own house.Will "sandwich" Houses Be Practical? The Forest Products Laboratory developed a sandwich building panel with a core of honeycomb paper. Treatment with synthetic resins makes the honeycombed paper resistant to moisture and decay. To study the suitability of such panes for house construction, a test structure was built some years ago at the Laboratory Exposure to Madison's rigorous weather for some time indicates that "sandwiches" will be suitable for use in buildings. Sandwich panels are now used in doors, partitions, furniture, and demountable buildings. In time they will no doubt be used in house construction.

　　Can Direct Seeding of Pine Be Improved? In the past, the replanting of burned-over or clean—cut forest areas has been done by the somewhat slow and laborious method of individual planting of seedlings which had been raised in tree nurseries. Direct seeding in such areas had proven unsuccessful because birds and rodents would help themselves to this ready supply of food before the seed could germinate. Now, discovery of a bird and rodent repellent that can be easily applied to longleaf pine seeds before sowing is- making the direct seeding of trees practical and inexpensive.

　　The repellent, composed of tetramethyl thiuram disulfide, is not harmful to birds or animals in the amounts used and does not retard germination of the seed. Although it is slightly irritating to the eyes, nose, and throat of humans, it is safe to use, according to studies made by the Alexandria (Louisiana) Research Center of the Forest Service and the U. S. Fish and Wildlife Service.

　　Direct sowing of tree seeds is the cheapest way to plant. Foresters, however, still advocate setting out seedlings because it is a simpler procedure for most people and more predictable. But seeding is becoming more foolproof and in another few years should be more generally accepted. Seeding costs about $ 8. 50 per acre compared to $ 12 per acre for planting seedlings.