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(1) the temperature of the center of the limbs changed much more slowly than that of the surface, and (2) the extreme daily variations were less. These points and also those brought out be. fore are shown in the diagram of observations made September 9, 1896. (Fig. 1.) The limbs were shaded until 1:15 P. M., when the screen was removed. Just before 2 P. M. the sky became cloudy.
The difference in temperature between the center and the surface of a limb can be explained by the fact that wood is a poor conductor of heat. The difference between the dead and live limbs can be accounted for almost entirely by the fact that the live limb contains much more water than the dead one. Water, having a high specific heat, varies in temperature much less rapidly than wood.
Thus far nothing has been said of the behavior of dead and live limbs when their temperatures approach the freezing point of water. Many observations were made on this point and all indicate the following conclusions: (1) The temperature of the air and of both the center and surface of a dead limb passes the freezing point of water without appreciable acceleration or retardation in its rise or fall. (2.) The temperature of the surface and center of a live limb remains near the freezing point for some time, but, having once got above this point, it rises nearly as fast as that of a dead limb. These points are shown in the diagram of readings for December 12, 1896. (Fig. 2.) The limbs were shaded all day.
This behavior is also to be explained, probably, by the presence of considerable water in a live limb and the comparative absence of it in a dead one. The "latent” heat of fusion must play an important part in retarding the melting of ice.
(Added since the above was read.)
Since the reading of the above paper a further study was made of the effect of water in controlling temperature changes in live and dead limbs. The dead limb and a section of the live one, containing the thermometers and corresponding in length to the dead one, were removed from the tree to the university greenhouse. The temperature changes in the two limbs, on their being moved in and out of the greenhouse, were noted for several days. The behavior was practically the same as when the limbs were attached to the tree. The dead limb was then soaked in water for some time and the temperature changes of the two limbs again observed during both rising and falling temperatures.
These observations show that the rise and fall of temperature of a dead limb is very appreciably checked on approaching the freezing point. In short, a soaked dead limb behaves like a live one, as far as temperature changes are concerned. There seemed also to be some indication that the temperature of the soaked dead limb, after having once passed below the freezing point, falls faster than that of the live limb below the same point. The later comparisons of the temperature changes of a live limb and a dead one not soaked are illustrated by the diagram for January 26, 1897. (Fig. 3.) A like comparison of a live limb and a soaked dead one is given by the diagram for February 26, 1897. (Fig 4.) In both these cases the limbs were placed out doors at 9 A, M., after having first acquired a uniform temperature in the greenhouse.
EXPLANATION OF PLATE I.
(Fig. 1.) Sept. 9, 1896.
Limbs shaded till 1:15 P. M., in sunshine till 2 P. M. Sky cloudy remainder of day.
(Fig. 2.) Dec. 12, 1896.
(Fig. 3.) Jan. 26, 1897.
No. 4 shows the temperature of surface of live limb.
(Fig. 4.) Feb. 26, 1897. No. 1 shows the temperature of air. No. 2 shows the temperature of surface of soaked dead limb. No. 3 shows the temperature of center of soaked dead limb. No. 4 shows the temperature of surface of live limb. No. 5 shows the temperature of center of live limb. Limbs placed outdoors at 9 A. M.
9 AM 47
9° 7 5 3o
DATA AS TO WIND-DISTRIBUTION OF SEEDS.
EDWARD M. HUSSONG.
Few matters are of greater economic importance than that of how and to what extent the seeds of flowering plants are distributed by winds. To the ecologist and phyto-geographer it is one of no moderate interest, as geographical distribution, though local, is in each of these lines of modern research no inconspicuous part; to the student of local flora it accounts partially for the unexpected appearance of species whose natural habitat has been assigned remote from his district of special work; while to the agriculturist it affects vitally his success or failure on the farm.
No available data touching directly upon the subject have been tabulated; perhaps none have been collected. Under my direction the students of the Franklin High School have carried forward for the past three years a series of field collections and laboratory cultures that have opened the problem at least to wider investigation. Our work briefly is thus:
We have made exposures of collecting traps in the various situations afforded us on the high school campus, around the homes of the students, and in the open prairies and fields. Leeward and windward positions were selected when previous indications foretold the direction of the wind; the value of these different positions is apparent from the widely different results obtained thus from the same period of observation. The different situations, as campus, barnyard, prairie, ravine, field, etc., give lawful variations which the observer can easily account for.
The traps used were deep tin cans, anchored fast by means of stout stakes to which the cans were securely wired in a manner allowing of easy detachment to remove the contents. Winds were grossly classified into four groups: breezes, local winds,