372 



Garden and Forest. 



[Number 395. 



to forest, to other vegetation or to topography. Examples 

 in three river basins, one of which contained fourteen per 

 . cent, of forest, another thirty per cent., and a third forty- 

 four per cent., all showed the same total flow-off for a given 

 annual rainfall, the varying forest areas seeming to have no 

 effect upon evaporation. The Connecticut showed much 

 less evaporation than the Potomac, with about the same 

 proportion of forest, but with a temperature of 2.7 degrees 

 lower, and generally evaporation was found to vary with 

 the mean temperature without regard to the amount of 

 forest. A great number of observations seemed to sub- 

 stantiate this theory, and the conclusions were that in New 

 England and the middle states the effect of forests upon the 

 total flow-off of the streams is not important enough to be 

 shown in the measurements. The influence of the tem- 

 perature of the air upon evaporation will be appreciated 

 when it is understood that the moisture which is held in 

 the air is doubled for each increase of twenty per cent, in 

 temperature. 



In studying the effect of forests upon the greatest and 

 least flow of streams no effect due to the forests was dis- 

 covered. The heaviest freshet usually occurs when the 

 ground is frozen and warm rain comes on a heavy cover- 

 ing of snow, or else in summer when a heavy rain falls 

 upon the ground already saturated. The rate of flow-off is 

 then determined mainly by topography. The lowest flow 

 occurs when the stream has for a long time been drawing 

 upon the stored ground-water, and has drained it to a point 

 below which it can be influenced by surface conditions. 

 The rate of flow is then mostly affected by the capacity of 

 the earth for holding water and its rate of yielding it up. 

 This is not a matter of vegetation, but of surface geology, 

 and for this reason it is thought the forests have little 

 effect upon the greatest or least rate of the flow of the 

 streams. 



These results, it ought to be said, were questioned by 

 some of the experts present, especially because there are no 

 instruments which give perfectly reliable measurements. 

 They are altogether negative, however, and they do not 

 imply that a covering of forest exercises no beneficial effect 

 upon the water-supply. Mr. Vermeule explained that his 

 studies make it clear that streams are often supplied for 

 many months entirely from water stored in the ground. 

 For example, in 1881 the Passaic River was supplied for 

 eight months in this way. With only rain enough to 

 make good evaporation, land in New Jersey will yield up 

 in nine months ground or spring waterequal to from 2. 29 to 

 7.59 inches of rainfall. Small barren redstone catchments 

 yield the least water, and the sand and gravel of the tertiary 

 formation the most. If the rain falls uniformly, from two 

 to two and a half inches a month may be taken into the 

 ground and discharged thence into the streams. The entire 

 rainfall of an average year, less the evaporation, could 

 be thus taken into the earth and none need flow over 

 the surface into the streams. Anything, therefore, which 

 affects the capacity of the earth to take up water and to 

 control its rate of discharge into the streams affects the 

 stream-flow by making it more or less uniform throughout 

 the year. And here the generally recognized good effects 

 of a forest-cover in holding back water until the earth can 

 take it up are seen. The basins which have the largest pro- 

 portion of forest invariably showed the best-sustained flow 

 in a dry season, although the total run-off was no greater. 

 The streams of southern New Jersey which have the most 

 forests are remarkabl)^ steady, the dry-season flow averag- 

 ing twice as much as that of the northern rivers. This is 

 due, undoubtedly, in large part to the absorbent power of 

 the sandy soil ; but a critical study of the daily flow of 

 these rivers shows that the Cedar swamps contribute largely 

 to the result. Should these be all cut off the streams 

 would certainly suffer and become more unreliable. The 

 conclusion of Mr. Vermeule's interesting paper is as fol- 

 lows : 



It will be seen that as to cultivated and forested catchments 

 our gaugings indicate the same total run-off for a given rain- 



fall, but a much more uniform discharge, fewer floods and 

 shorter dry periods on the forested areas. Forest streams are 

 consequently more valu.^ble and reliable for power, and for 

 water-supply they require less storage capacity to provide for 

 a given ddily draught. ' The waters are also much less likely 

 to become muddy or otherwise contaminated. The worst 

 condition of all for a catchment is barrenness. Barren earth is 

 non-absorbent. The water soon fails to penetrate it and oxi- 

 dizes its fertilizing constituents. Heavy rains run over the sur- 

 face, wash off ail the loose materials, and barren conditions once 

 begun perpetuate themselves. There is always danger of 

 such coniiiiious when slopes or other areas unfit for cultiva- 

 tion are deforested, and there is special danger where forest 

 fires are prevalent. There are a few small red sandstone areas 

 in New Jersey now in this condition, where the streams dry 

 up for weeks in succession to become torrents when the rain 

 falls in considerable quantity. Compared with barrenness, 

 cultivation is harmless to the stream. Our end, therefore, 

 should be to keep all ground unfit for cultivation clad witli 

 forest. 



Cladrastis. 



IN 1824 Rafinesque published his Neogeiiilon, a pamphlet 

 of four pages, in which he characterized sixty-six new 

 genera of plants. The first of the list is Cladrastis, pro- 

 posed to receive the leguminous tree which the elder 

 Michaux had discovered in 1796 and named Virgilia lutea. 

 No reference to an earlier publication of Cladrastis is made 

 in the Neogeniton, except the general introductory remark 

 that some of the new genera " were indicated last year, 

 1824, in the catalogue of the Botanic Garden which I have 

 tried in vain to establish in Lexington." Dr. Call, in his 

 exhaustive Life a7id Wri/ings of Rafinesque, recently pub- 

 lished by the Filson Club, of Louisville, Kentucky, does 

 not include this catalogue in his list of Rafinesque's writ- 

 ings, and probably it was never published ; but in the first 

 volume of the Ciiicinnali Literary Gazette, published in 1824, 

 which has recently come into m)' hands for the first time, 

 the genus Cladrastis is carefully described on page 66, 

 issued February 21st, and this, therefore, is an earlier pub- 

 lication of the genus by a year than that in the Ncogenilon, 

 and it is probably the earliest. On the same page of the 

 Cincinnati Literary Gazette the species is mentioned as Clad- 

 rastis fragrans, which thus becomes another Synonym of 

 Cladrastis lutea of Koch, Virgilia lutea of Michaux, and 

 Cladrastis tinctoria of Rafinesque in the Neogeniton. 



c. s. s. 



Notes on some Arborescent Willows of North •* 

 America. — II. 



Salix taxifolia, H.B. K., southern Arizona, Rillita River 

 (Pringle, 1883), Santa Rita Mountains (Professor Tourney). 

 — A moderate-sized tree, thirty feet in height, with delicate 

 spray, the lower branches drooping. Compared with ex- 

 treme Mexican forms of the species, for instance Dr. 

 Palmer's specimens (1193) from Colima, there is in the 

 Arizona plant more or less variation in the direction of 

 Salix longifolia. But S. taxifolia, like other members of the 

 group to which it belongs, is exceedingly variable. The 

 fertile aments in Mr. Pringle's specimens are rather oblong- 

 cylindrical than "sub-globose," and in both the Arizona 

 collections the leaves are larger. Nevertheless, the nar- 

 rower and longer aments are more than matched by Mr. 

 Brandegee's specimens from Lower California, otherwise 

 characteristic taxifolia ; and the larger leaves are appar- 

 ently only the result of a less starved and stunted growth. 

 A form collected by Mr. Pringle "in the valley near Chi- 

 huahua" is identical with his Arizona specimens. 



Salix lasiandra, Bentham, var. caudata, Sudworth, Bull. 

 Torrey Bot. Club, xxii., 43 (1893). S. lucida, var. lanceolata. 

 Hooker, Ft. Bor.-Am., if, 148 (1839). S. pentandra, var. 

 caudata, Nutt., Sylva, i., 6r, t. 18 (1842). S. Fendleriana, 

 Andersson, Proc. Am. Acad., iv., 54 (8) (1858). S. lasi- 

 andra, var. Fendleriana, Bebb, Watson & Brewer, Bot. Cat., 

 ii., 84 (1880). 



Mr. Sudworth is right ; the older name of Nuttali 



