meteorological conditions must be accessible, samples of which I have prepared for twenty United States stations." If we suppose some wheat to have been sown on the 22d of September, 1871, near Paris, and if we adopt the rule established by Gasparin that the vitality of the seed is actively aroused as soon as its temperature in a moist earth exceeds 5° C., and that it germinates visibly when it has received a sum total of mean daily temperatures that is equal to 85° C., and that the sprout rises above the surface of the earth in a few days after the seventh, then we obtain six days as given in the following table for the interval from sowing to germination. A similar computation for every other date of sowing, as given in the following table, shows at a glance the effect of the temperature of the soil on this phase of plant life. Duration, in days, from sowing to germination of winter wheat at Montsouris, France, for the years 1872-1881. Germination. Average dura Date of sowing. 1871. 1872. 1873. 1874. 1875. 1876. 1877. 1878. 1879. 1880. 1881. tion Aver In studying the preceding table we recall that the duration of germination varies slightly with the condition of the soil and the depth of the grain below the surface; these two considerations will be perfectly allowed for if we observe directly the temperature of soil by a buried thermometer. Such observations are earnestly recommended to all agricultural experiment stations, as they are, evidently, more directly applicable to the growth of plants than any crude a These tables are omitted in the present edition. approximations derived from the observation of the temperature of the air only. If when the grain has sprouted the soil continues very dry, the nourishment having all been drawn from the seed, the young plant may droop and die. If, again, the frost penetrates to the seed while it is germinating, many of the seeds will perish, and the field will appear as if sparsely sown, but this latter mishap is generally repaired by nature if the soil is good and the springtime favorable, for the sowing is generally in excess and the extra heading will supply the loss of the seeds that have perished, but in poor soil the harvest will be notably diminished, and often it will be profitable to plow the soil for a new sowing. In any case the chances for a successful crop vary very much with the date of the sowing, as we shall see by the study of the following table, which shows that in each year the season for sowing that is favorable to the crop of that year is very much restricted by the early arrival of the winter cold. Thus in 1871 the sowing was stopped on the 20th of October by the cold weather; in 1872 it continued throughout the autumn until the 29th of December; in 1880 it occurred on the 3d of November. Sometimes heavy rains prevent the sowing, but in 1881 neither cold nor rain prevented field work until the middle of December. [In order to save space I have omitted the elaborate tables of frosts, low temperatures, and rains given by Marié-Davy for each of these years and weeks.—C. A.] The grain now arrives at the epoch of heading, at which the original stalk becomes several branches, each of which bears an immature head on which the rudimentary seed can already be counted under the microscope; the number of such seeds will not increase in the further development of the plant, but many of them may not come to maturity; therefore a careful count of these rudimentary seeds over a small area of the field would give a first estimate of the maximum possible crop. According to Gasparin the length of time that elapses from the moment when the mean daily temperature of the air in the shade is 5° C. up to the date of heading of the wheat is such that the sum total of the mean daily shade temperatures is 430° C., but as the initial date is difficult to determine we shall in our calculations adopt the rule of Hervé Mangon, according to whom the sum of the mean daily temperature in the shade, rejecting all that are below 6° C. (at which the wheat does not vegetate), is 640° C. if we count from the date of sowing, or 555° C. if we count from the date of germination. The following table is computed by counting from the former date; a parallel computation from the latter date shows that on the average of ten years there is no appreciable difference between the results. Duration, in days, from sowing to heading of winter wheat, at Montsouris, France. Average for 1872-1881. Date of sowing. 1872. 1873. 1874. 1875. 1876. 1877. 1878. 1879. 1880. 1881. 1882. This table shows that on the average of ten years the seed that was sown, e. g., on the 27th of October and required one hundred and fifty-five days to head, is that which took the longest time; for sowings before that date, as well as after it, the durations steadily diminish; in other words, this sowing is that whose development was the most retarded by the winter cold. If we compare this table with those given by Marié-Davy, showing the frosts, we find a complete inversion in the chances of injury from frost; wheat as a green plant has as little to fear from frost as has the dry grain. But during and after the formation of the embryo seed, as well as during germination, on the contrary, frost is very injurious, and if the embryo is seized by frost it perishes. If this accident occurs it is possible that the progress of heading may permit a new formation of embryo to replace those which have perished. Such accidents must have occurred to the seed sown in the hope of reaping an early harvest in 1874, 1875, 1876, 1877, 1878, and 1881, but did not occur in 1882. This accident is not incompatible with an excellent harvest, as we see in the case of 1874, but it causes a decided retardation of the harvest, as in 1877. The mean of the ten years shows that the heading occurs at an epoch in the spring when the mean temperature of the air is between 6° and 13° C., and when the rainfall is generally abundant, so that at this epoch damage does not generally occur to the grain; only in case of the sowing of September 29, 1878, did the heading occur during the very cold season likely to be injurious to vegetation. We pass now to the period from the heading of the wheat to the flowering. According to the determination of Herve Mangon, the sum total of the mean daily air temperatures in the shade necessary to flowering is 1,500° C., counting from the date of sowing, or 860° if counted from the date of heading. If we consider the date thus fixed for the flowering we shall find that it corresponds to a mean daily temperature at that epoch of 16.5° C. on the average of many years; but if we consider the individual years we shall find the actual mean temperatures of that date to vary from 8° to 22° C., and also that for temperatures below 13° the flowering becomes uncertain, prolonged, and detrimental to the crop; but as to the upper limit, 22° C., there is no evidence that even higher temperatures will be injurious. The following table gives the calculated number of days that elapse from the sowing to the flowering, together with the average duration and the corresponding average date. The corresponding tables of mean temperatures and lowest temperatures at the date and the quantity of rainfall are omitted for want of space. Duration in days from the sowing to the flowering of winter wheat at Montsouris, France. Average for 1872-1881. Date of sowing. 1872. 1873. 1874. 1875. 1876. 1877. 1878. 1879. 1880. 1881. 1882. November 17 214 211 November 24 December 1.. 212 212 219 207 207 208 208 213 200 203 202 202 206 193 200 195 195 199 188 197 December 15.. 186 194 188 188 192 184 190 December 22. 179 189 181 181 186 177 183 197 183 186 183 184 December 29. 172 185 178 178 180 171 176 191 176 181 176 179 203 209 231 217 211 212 214 June 19 198 206 224 211 The ripening of wheat is perfected when the plant has received a sun. total of mean daily air temperatures in the shade of 815° C. since the date of flowering. This result happens on the average of Paris forty-four days after flowering, and the individual irregularities scarcely ever exceed four or five days. Therefore the date of flower ing can be made the basis of a very close estimate of the date of ripening. The date of flowering occurs at the time of the greatest vital activity of the plant, which at that time is actively drawing its nourishment from the soil and is transpiring, assimilating, and increasing in weight. But very soon this work is relaxed and is confined more and more to the interior of the plant, conveying into the seed the elaborated materials formed within the leaves and stems. It is especially in this latter part of the life of the plant that the internal consumption can exceed the gain from without, and the plant tends to diminish its dry weight. This period has a great influence on the final result, not only because the plant can gain as a whole, but especially because of the distribution which is made within it of the material which it has brought together. The straw has only a secondary value. It is the seed which constitutes nearly the whole value of the harvest. Therefore all that passes from the straw to the grain is a benefit, though this passage should be accompanied by a notable consumption of the nutritious materials of the stalk. It is neither the state of preparation of the stalk, nor the heat, nor the radiation, nor the moisture which of itself alone produces the best quality of grain. There must be a reunion of all these various elements in a proper proportion, which latter will vary with the weather and with the locality even with the same weather. The blighting of wheat is an accident that one dreads most at this period. The blight, properly so called, is due to a temperature and a radiation that is too intense for the movement of the sap in the plant; the seed has not time to receive the sum total of the nourishing particles that have been prepared for it; therefore it becomes small, lean, and shriveled up. A greater sum total of moisture in the soil or a less active transpiration would have given a better result. But we often confound the blight, properly so called, with the analogous result produced by an insufficient assimilation or elaboration of the various materials that go to make up the wheat grain or by a disproportion in the relative quantities of the elements that should make up the seed. The following table shows the number of days elapsing from sowing to ripening for the dates adopted in the previous tables. It is calculated by first ascertaining the number of days elapsing from flowering to ripening according to the rule above given and then adding these intervals to those already calculated for the flowering. |