Octobe;r 5, 1888.] 



SCIENCE. 



161 



of tlie war department, and are especially interesting for the pic- 

 tures they preserve of the vast area between the Missouri River 

 and the Pacific Ocean before it became accessible to any except 

 military expeditions, specially equipped exploring parties, trappers, 

 and missionaries. Adjoining this section are complete sets of the 

 reports and publications of the several surveys that preceded the 

 National (Geological Survey, and from the combination of which it 

 was organized, — the Hayden, Powell, King. Nothing needs to be 

 said of the practical value of this collection. The work of all of these 

 surveys is being embodied in the maps prepared under the direc- 

 tion of Major Powell, and a large portion of it is found available, 

 and adaptable to the uniform system adopted by the National Sur- 

 vey. These comprise all the official geological reports ; but they 

 are supplemented by a very full collection of United Stales Govern- 

 ment reports on miscellaneous sulijecls, principally the resources 

 and industries of the United States and of detached portions of the 

 country. The National Survey itself, or different members, includ- 

 ing Major Powell and several of his chief assistants, have made 

 valuable contributions, in the form of reports, monographs, or bul- 

 letins, to our knowledge, especially of the resources of the less- 

 understood portions of the country; and some of the most impor- 

 tant work now in progress under the direction of the Naliona 

 Survey has to do directly with economic subjects. 1 



Lastly, in the division of official reports, are those of foreign 

 countries. Canada has an excellent geological survey, and its pub- 

 lications are very valuable. European reports are arranged geo- 

 graphically, beginning with those of Russia. France and Germany 

 have no geological surveys, but their commissions to make geologi- 

 cal maps of those countries have made important reports. The 

 collection of foreign reports is large. 



Second in importance to the division of official reports, is the 

 excellent collection of the transactions and proceedings of geological 

 societies, those of scientific societies, and bound files of scientific 

 periodicals. These occupy a large space in the library, and are 

 constantly put to practical use. 



The library has been recently enriched by the purchase in Paris 

 of six hundred and twenty-five volumes, a part of the private libra- 

 ry of Desnoyers, a distinguished geologist and writer, and libra- 

 rian of the Paris Museum of Natural History. Many of these books 

 are presentation copies, containing the autographs of their authors. 

 The books purchased comprised nearly all offered in the divisions 

 of geology, coal, glaciers, artesian wells, volcanoes and earthquakes, 

 the geology of individual countries, mineralogy, and paleontology. 

 Many of these books are rare, and their acquisition greatly enriches 

 the library. A carefully selected general reference-library com- 

 pletes our survey. 



In the bibliographical department a card-catalogue of authors, 

 embracing the entire library of books and pamphlets, and consist- 

 ing of several hundred thousand separate entries, has been finished. 

 In addition to this, there is now in process of preparation a bibli- 

 ography of North American geology, — a work that will require 

 several years to finish, — and also a bibliography of the oificial 

 geological reports of the States and of the United States Govern- 

 ment. The work upon the latter has been about one-third done. 



Probably there is no department of the National Survey library 

 more highly prized than that of maps. Of these there are about 

 twenty thousand, arranged geographically in drawers which admit 

 of their lying flat. None of these are maps made by the National 

 Survey, but they have been gathered from every available source, 

 and constitute the largest and best collection of maps in the United 

 States. A complete catalogue has been prepared, and the larger 

 part of the maps are mounted on linen. 



The library is admirably housed. The room devoted to its use 

 is well lighted and ventilated, and not only admits of a most ad- 

 vantageous arrangement of the books, but it also affords e.xcellent 

 facilities for the work of the librarian's assistants, and conveniences 

 for those who have occasion to consult the books. 



The Influence of Light upon Tree-Growth. 



Among the interesting discussions to be found in Professor Fer- 

 now's second annual report on forestry is a brief consideration of 

 the influence of light upon the development of various trees of the 

 forest. The following extracts give the essential portions of it ; — 



" It is a well-known fact that light is necessary for the develop- 

 ment of chlorophyl, and therefore for the life of all green plants, 

 and especially for tree-life and wood-formation. Heat alone, which 

 practically always accompanies light, is not sufficient for this purpose, 

 although it is still an open question as to what the absolute light- 

 requirement of a tree species may be, or how much of the effect of 

 increased light on growth is attributable to the light alone, and how 

 much to the accompanying heat. Yet it is undeniable that there 

 exists a relative difference of light-requirement, not only for differ- 

 ent species of trees, but for all other plants. 



" In last year's report I alluded to this difference in regard to the 

 forest-weeds, which serve in forest management as an indication of 

 the amount of shade which the trees exert, and with that their ca- 

 pacity of impeding evaporation from the soil. While the rosin- 

 weed, sunflowers, some of the golden-rods {Solidago nemoralis), 

 and some of the meadow-grasses, and the fire-weed {Erechthites 

 liieracifolia), may be mentioned as requiring full sunlight for their 

 best development, the Indian pipe {Monolropa) is most decidedly 

 averse to a high degree of light. The partridge-berry {Mitchella 

 repens), and among the grasses Poa flexitosa, brevifolia, Festttca 

 nutans, Cinna arundz'nacca, may be named as seeking the shade. 

 The ground hemlock and rhododendron are also characteristic 

 shade-plants. By careful observation we could make a classifica- 

 tion of weeds characterized by their dependence for normal devel- 

 opment on various degrees of light and shade. 



"The frequently observed change or 'alteration' of the flora, 

 when the original forest is removed, must to some extent be ex- 

 plained by this light-influence. 



" The amount of light required is, however, considerably modi- 

 fied by other influences of site. Where the intensity of the sunlight 

 is gieat, as in southern countries, in higher altitudes, and in dryer 

 climates, and also where the growing season is longer or the num- 

 ber of sunny days greater, a shade-enduring species will be able to 

 sustain still more shade, and a light-needing one may even become 

 shade-enduring. The flora of high altitudes, therefore, is in general 

 decidedly light-needing. The elms, oaks, and ashes, which in 

 northern latitudes are clearly light-needing, may in southern lati- 

 tudes endure considerable shade. 



" Trees are no exception to this rule ; and while nearly all de- 

 velop best, i.e., make the most wood, in the full enjoyment of light, 

 their capacity of preserving their vitality and of developing under 

 the shade varies greatly. While the yew will thrive in the densest 

 shade, a few years of overtopping will kill the larch ; so, also, while 

 the beech will grow with considerable energy under the partial shade 

 of such trees as ash, maple, etc., the oak will only just keep alive 

 under the same conditions, and some of the birches would die. 



" Favorable moisture-conditions make all species less sensitive to 

 the withdrawal of light ; and here, perhaps, the influence of the 

 heat which accompanies the sunlight plays an important part. 

 Therefore, on the fresh soils of bottom-lands, on northern expos- 

 ures, and in the coves and depressions in the mountains, the light- 

 needing species will be found to suffer less from shading than on 

 dry, poor soils. Even so shade-enduring a species as the spruce 

 becomes sensitive to the withdrawal of light when growing on dryer 

 mountain-sites. 



" The observations by which we may arrive at a relative classifi- 

 cation of our timber-trees with regard to their light-requirements 

 must therefore be made with due consideration of these modifying 

 influences. The capacity to withstand shade, even in later life (in 

 their youth most trees will stand considerable shade), is noticeable 

 in the denser or less dense foliage, and in the capacity of overtopped 

 individuals or overshaded branches to preserve their vitality for 

 a longer or shorter time. The observations on this line must, then, 

 be made in the dense forests, in order to be able to judge of their 

 characteristic foliage-development in the shade; for, if grown in 

 the open, so much light is accessible to every part of the crown, 

 that leaf-development, even in the interior of the crown, is unim- 

 peded, and quite a dense foliage is the result. Thus, in the open, 

 the maples, elms, sycamores, black locusts, etc., make good shade- 

 trees, while in the elense forest they thin out and have but scanty 

 foliage. The conifers, which, like the spruces and firs, preserve 

 the foliage of several years, have perhaps the greatest capability of 

 growing under shade, and preserving their foliage, in spite of the 



