THE GARDENERS' CHRONICLE OF AMERICA. 



137 



assists somewhat in keeping the central portion of the 

 street clean, as dust and dirt are more easily swept to the 

 gutters by rain, winds and passing traffic. As far as the 

 use of a pavement is concerned, it w-ould be more desirable 

 to have it level in cross section, and under certain condi- 

 tions safer. A vehicle turning on the outward sloping- 

 crown of a road is pitched in the wrong direction, and if 

 the pavement is slippery, tends to slip or skid. The outer 

 rail of a railroad is raised on curves to assist in turning 

 the curve and the belter to resist centrifugal force. On a 

 street pavement the inner rail, so to speak, is raised, and, 

 according to any method of construction yet developed, 

 necessarily so. The problem is to reduce the crown as 

 much as practicable and establish reasonable rules for 

 distriljuting the pitch fairly evenly across the width of 

 roadway. The character of wearing surface has much to 

 do with the amount of crown permissible. 



The following list of pavement surfaces is arranged in 

 the order of amount of allowable crown : 



Water-bound macadam — Oiled and tarred macadam 

 (surface treated) — Stone blocks — Brick — Bituminous 

 concrete (mixed before laying) — Sheet asphalt — Creo- 

 soted wood blocks — Portland cement concrete. 



In this list creosoted wood block is put near the bottom 

 because it is a slippery pavement surface and needs a flat 

 crown. Also, by reason of the true surfaces and gauged 

 size of blocks, it can be laid close to a theoretical grade. 

 Portland cement concrete is put at the bottom of the list, 

 not because it is slippery, but because on account of con- 

 struction methods it can be screeded or struck to a fairlv 

 exact grade, whereas otlier plastic pavements, bituminous 

 concrete and sheet asphalt, cannot be made so exact on 

 accoimt of the necessity of rolling after spreading to se- 

 cure compression. 



If the longitudinal grade of the pavement is practically 

 level, the crown must be greater at catch-basin inlets than 

 at gutter summits between inlets, unless the grade of the 

 center of the roadway is carried up and down with gutter 



grades, which is not a desirable method. Un streets with 

 longitudinal grades requiring water in gutters to flow all 

 in one direction, and on country highways where drainage 

 is carried away by surface ditches, the crown may be 

 made the same at all points. 



'1 he cross section of a pavement may be a segment of a 

 circle, parabola, or two inclined planes connected with a 

 segment of curve. Either of the two latter fornts is pre- 

 ferable to the first, because a segment nf a circle makes 

 the pavement fairly flat in the center and grows unpleas- 

 antly steeper near the gutters. The inclined planes or 

 parabola "get away" on a quicker slope from the center 

 and do not so materially increase as the gutters are ap- 

 proached. Traffic, then, will use all parts of the paA^ement 

 with fairly equal facility and ease. 



\\ hatever theoretical crown or cross section is adopted, 

 it should be remembered that in actual construction the 

 cross section will be only approximated. It is not prac- 

 tical to set enough grade points or to maintain them care- 

 fully enough to attain the theoretical section. 



In ])ractice, in setting grades for crown or cross sec- 

 tion, it is common to adopt a rule of measuring, say, one- 

 half the distance from the center and dropping one-fourth 

 the total crown. This will give a segment of an all-curve 

 cross section. Another rule may be to measure two-fifths 

 the distance from the center, drop one-fourth of crown 

 and thence straight to the gutter. Other modifications of 

 such simple rules may be devised, using three points on 

 wide roadways between center and gutter, approximating 

 more closely to a true parabola or providing longer in- 

 clined planes and shorter connecting curve. It is some- 

 times advised to increase the crown on pavements having 

 considerable longitudinal grades, thus carrying the water 

 more quickly to the gutters. The opposite practice is gen- 

 erally better — to decrease the crown on steeper grades. 

 There are 'two reasons for this — the tendency to slip or 



'.'§k.id is less, and the washing or cutting action of water is 



j-4.ess 'on the increased crown section. 



Horticulture at the Panama-Pacific Exposition 



By G. A. Dennison. 



The growth (if the great industry txpified by the De- 

 partment of Horticulture at the Panama-Pacific Inter- 

 national Exposition can be better appreciated when we 

 realize that it was found necessary at this exposition to 

 devote an entire department to its portrayal — a recogni- 

 tion w'hich has never before been accorded to horticulture 

 at an international exposition. The com]irehensive scope 

 of this exhibit, the plan underlying it all, and the artistic 

 presentation of the "best of the best" from the horticul- 

 ture of the many nations participating will make it his- 

 toric as well as vastly entertaining and instructive to all 

 who join the exposition's throng. 



The aim of the department has been to present the ad- 

 vancement which has been made in the past few years by 

 each branch of the horticultural industry. From wdiat is 

 known as the great back-to-tlie-land movement, the crea- 

 tion of fine country estates and the advance of scientific 

 application to horticultural pursuits, there has arisen an 

 insistent demand for orchard products of the highest 

 merit, and for a more comprehensive treatment and a 

 more intelligent application of ornamental trees and 

 shrubs. The making beautiful of a practical thing is a 

 great influence spreading over the country. 



The horticultural exhibit will include displays from 

 Japan, England, Scotland, Ireland, Australia, New- 

 Zealand, The Netherlands, France, Argentine, Cuba, the 



['hiliiipines, Hawaii, and the following States of this Con- 

 tinent : Oregon, Washington, Utah, Idaho, Montana, 

 Nevada, California, Colorado, Kansas, Missouri, Ar- 

 kansas, Illinois, Iowa, Indiana, Ohio, New York, Massa- 

 chusetts, Rhode Island, Pennsylvania, New Jersey. 

 Florida and Maryland. 



The general plan of this exhibit is based on three di- 

 visions : The outdoor, the conservatory and the economic 

 display. 



A garden of nine acres lying to the south of the Palace 

 of Horticulture and in front of the Inside Inn has been 

 set aside for the outdoor exhibits. Every participating 

 State and nation have part of its horticultural display in 

 this garden. The Netherlands and the State of Massa- 

 chusetts make their displays exclusively in this section. 

 Holland's unified exhibits are presented under the aus- 

 pices of the National Board of Horticulture of the Neth- 

 erlands, personally represented by their expert, Airie Van 

 \'liet, and is of such character as to represent the quintes- 

 sence of the floral culture industry of that country. The 

 material shown was commandeered by the national or- 

 ganization, so that only the finest specimens are on dis- 

 play. Not one member of the organization is adverti'^ed 

 — it is a collective display representing the growers as a 

 whole. 



A flowering mass of 60,000 bulbs is but an item in this 



