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to seriously reduce the crop of fruit. The most disastrous storms are probably those milder ones of long duration, and which are accompanied by a low temperature. Not only may such weather tend to prevent the discharge of pollen, but it prohibits the work of insects.
It must be admitted that the above remarks are inferences. We have almost no exact knowledge upon the effect of rain storms upon the setting of fruit. A few small studies have so far been made in this country, and these are now quoted.
Beach and Fairchild* report experiments in applying continuous sprays to pears and grapes. "On May 16 two Mount Vernon pear trees, apparently of equal vigor, standing within one hundred feet of each other, were selected. Into one was thrust the Vermorel nozzle, with its broad, fine spray. The tree was about twenty-five feet high, and the spray from the nozzle did not entirely cover it; in fact, the original design, soon abandoned, was to wet only one-half of the tree, and leave the other half dry. At the inauguration of the experiment, only a few blossoms had opened upon either tree, and, as no insects had been busy about the fruit trees, owing to the cold weather immediately preceding, no risk from previous pollination was run. The water was turned on at noon of May 16, and kept running (except from 10 A. M. of the 21st, to 10 A. M. of the 23d, during an almost constant rain-storm, pre
*Eleventh Ann. Rep. N. Y. State Exp. Sta. for 1892, 007.
of the 25th.
Rain at Blossoming-time.
cipitating .72 of an inch of water), until 3 P. M. The total length of time in which the tree was kept wet was two hundred and nineteen hours, or nine days and three hours.
"On May 17, after the tree had been under the spray twenty-four hours, an examination was made of the stigmas of many of the flowers, and they were found to be dusted with pollen, although no insects had been seen about the tree. Pollen was taken from fresh anthers on the 21st (the fifth day), and placed in weak sugar solution, to test its germinative power. It proved to be perfectly capable of germination. The flowers at this time presented a curious appearance. The anthers of the innermost stamens were plump and of their normal pink color, while the outermost ones were swollen and decayed, and contained many disintegrated pollen grains, and a few that had evidently been induced to germinate by the excess of moisture. The power of the male elements to withstand long-continued moisture was apparently great, for at the close of the experiment, after the rain had ceased, many anthers opened and shed an abundance of pollen, while the anthers of flowers on adjacent trees had withered and fallen several days previously. After turning off the water, on the 25th, an examination with a hand lens was made of flowers on both the side nearest to and that farthest from the spray, with the following result:
"Of four hundred and three flowers counted on the side receiving the most water, one hundred and three were possessed of plump anthers and apparently
normal stigmas. Of three hundred and three flowers upon the dryer side, only three were still fresh and capable of fertilization. The effect of the water in retarding the development of the flowers was strikingly illustrated.
* * * * * * * * * * *
"Although, as mentioned above, after the spray had been removed many flowers with perfect anthers and pistils remained capable, presumably, of self-pollination, only one fruit, bearing three seeds, was borne by the tree. This was produced about midway between that half more heavily wet down and that more nearly dry. The unsprayed tree produced a fair crop of normal fruit.
"Two vines situated near each other were selected for an experiment. One was left untreated for a check, the other was sprayed for twelve nights and days. Since the Duchess came into blossom later than was anticipated, the sprayed vine was under treatment a week before the check began to bloom. Unavoidably the spray was discontinued before either of the vines was out of blossom. It will, therefore, be seen that the twelve days' treatment did not cover the entire period that the vines were in bloom.
"The first apparent effect of the spray was to retard the opening of the grape blossoms four days, as compared with the blossoming of the check vine. This effect was noticeable during the blossoming period, and the treated vine continued in blossom at least four days longer than the check. Retarding the blossoming period, however, had no perceptible
Rain at Blossoming-time.
influence on the ripening of the fruit, for the fruit of both vines ripened at the same time. * * *
"A microscopic examination, made after the spray had been running eleven days, failed to disclose any perceptible injury to the pollen. The pollen germs were not disintegrated, nor had they germinated, and no difference could be detected between them and pollen grains from the check vine. By its peculiar structure the grape blossom is well adapted to withstand protracted rains without injury to the sexual organs. As shown by one of the writers in a recent paper (see page 230), many grapes pollenize their own stigmas before the blossoms open enough to allow the entrance of outside pollen, and the Duchess belongs to this class. Although self-pollination is thus insured, efficient fertilization does not always follow, and consequently in some varieties it does not result in the production of fruit. grapes are able to set fruit only when supplied with outside pollen. It is, therefore, probable that with grapes of this class, e. g., Salem and Brighton, the effect of constant spraying throughout the blossoming period would give more marked results than with the variety noted in this experiment.
"The most marked and permanent influence of the spray was seen in the character of the fruit. The clusters from the treated vine had very many abortive berries, either with no seeds at all or with only mere rudiments of seeds. A few clusters were nearly or quite perfect. These may have blossomed after the spray had been discontinued. All other
clusters had many abortive fruits, and showed every gradation of loss up to 80 or 90 per cent. No cluster was seen in which all the berries were abortive. With the check vine perfect clusters were numerous, and abortive berries were comparatively few. whole loss of fruit on the sprayed vine cannot be computed by comparing the amount of perfect with abortive fruit, because some blossoms must have failed to form even abortive fruit, and some of the abortive fruits dropped before the grapes were gathered. It should be borne in mind, therefore, that the total loss of fruit from the spraying is not represented in the following figures. A comparison of the fruit of the two vines shows the following results:
"1. Counting all berries, whether perfect or abortive, the average weight of a berry from the sprayed vine was 8.5 grains, and the average weight of a berry from the check vine was 17.5 grains, showing a difference of 106 per cent.
"2. The amount of abortive berries was compared with the perfect berries of each vine, and 60 per cent of the fruit from the sprayed vine was abortive, while but 21 per cent of the fruit from the check vine was abortive."
Halsted has also made observations upon the influence of weather upon pollination, and finds that continued wet weather at blossoming time seems, in most cases, to lessen the setting of the fruit.
*Special Bull. C, N. J. Exp. Sta. (1889), and Rept. for 1889, p. 230, and Rept. for 1890, p. 330.