DAYLIGHT AND PLANTLIFE

Dominion, Volume 14, Issue 37, 8 November 1920, Page 5

DAYLIGHT AND PLANTLIFE

« A REMARKABLE DISCOVERY LIGHT. NOT HEAT, DOMINATING FACTOR IN GROWTH. For generations scientists have known, that sunlight was necessary for tho normal growth of most kinds of plants. I hey assumed that, although summer weather might at times become too hot for certain Isinds, sunlight in itself could never causa any injury, except perhaps the injury duo to burning. The discovery that apart from any effect of burning it is possible for plants to have 100 much daylight—or, in other words, too many hours of daylight in comparison with the num'bors of hours of darkness—was mado recently by W. W. Garner and H..A. Allard, of tho Bureau of Plant Industry, United States Department of Agriculture. They have 6hown that too long a day as well as too short a day can prevent many kinds of plants troni evier reaching their stage of flowering and fruiting. The advance in agricultural practice which may come through this new discovery will have to be brought about largely by plant breeders and other crop specialists. For instancy, it will provo of material significance in the future planning of crop 9 for different regions, especially whero consideration of new crops for a given latitude is necessary. This new principlo also undoubtedly explains tho erratic behaviour which has been observed of many crops wlien shifted to different latitudes. It may tend to clear up the conflicting results of variety testa and field tests conducted with tho samo crops but in different lvgi'oms. Tho experiments have shown, for instance, {Bat ragweed requires for floweriii" a stimulons afford wl by the shortening of the days and lengthening of the nights. It does not como into flower until tho period of daylight falls below fifteen hours. In tho latitude- of Washington that hnppenrxl about July 1. But of the ragweed seed should bo taken to

northern Maine and planted the planM j would not experienca a length of day licloiv fifteen hours until about August '1. Therefore, they could not come into ilower until after August 1, and, though tho vegetable growth might bo very rmiV. tlmv conlit not mature -seed before killing frosts. Thvs long days, therefore, make it impossible for ragweed to perpctuato itself in fliat latitude. _ On the other hand, plants that get their flowering stimulus from a long day could not perpetuate themselves through seed tormation at the equator. "Tho intensity of tho light has very much more fiigmiiconce upon iho growtn of the plnnt than hus usually been supposed," said Mr. Garner in speaking of his Uhoory. "Greenhouse experiments prove that the (lowering and fruiting period of practically any plant can be mado to take place at any timo of the year by darkening tho greenhouse in tho morning and evening if the day is too long or by lengthening the day by artificial light if t]io day is too short. Ho expected* he said, that florists and grcenhouse'operatora would use the new method of controlling flowering and fruiting ol plants. Two Seasons for Violets.

For example, wo all know that tho prico of violets during certain ponods of the year is very high. . ihat is because 'iihey bloom only during tho comparatively short days of the spring Howover if tho violot plants are covered with light-proof boxes at night and not uncovered until the sun is about half an hour high each morning during the summer time, violets can be forced to bloom again in the summer. "Spring flowers and spring crops happen \b 'bo spring flowers and spring crops because tho days at tho season oi their flowering and fruiting have tho propel number of hours of daylight. Correspondingly, the early summer flowers and crops'must have a longor period of daylight. This line been proved as to a large number of plants, and scLcntista believe tint tho principle will hold throughout tfie higlier forms of plant life, and that, it may be applicable to animal lifo a3'well. ; "The plant cannot accomplish reproduction, it has been shown, except when it is exposed' to a favourable length of daylight. The requirements, however, diffor widely with species and varieties. But a length of day that is unfavourable to reproduction may be favourable to growth. . tinder that condition tho plant continues its vegetative development profusely and indefinitely without bearing fruit. A length of day may bo found that is favourable to both reproduction and vegetative 'growth. That tends to bring about tho 'ever-bearing' type of fruiting. Startling things 111 plant life have been accomplished by employing dark chambers to shorten the period of light or artificial lights to extend it. Department of Agriculture experts have shortened or lengthened tho life-cycle of plants, have made some of them complete two cycles in a Bingle season, have brought dt'hlers into ilower and IVmt months in advance of their regular time, nnd with still others have greatly delayed and even prevented fruiting. Long series of tests havo been made with soy beans, tobacco, wild aster, climbing hemnweed, beans, ragweed, radish, carrot, lettuce, hibiscus, cabbage, violets, goldcnrod, spinch, cosmos, iris, lioggartick, buckwheat, and various other plants.

Speeding Up the Bean. 'A tesE made with soy beans will show how the principle works. For the test plants the day was shortened by several hours. That is they were exposed to the light only from 10 o'clock in tho morning till 3 o'clock in tho afternoon. They were first placed in tho dark house on Alay 21. Control plants, otherwise treated exactly like the test plants, wero left exposed to the light Urom dawn till dark. The first blossoms appeared on tho'dark-house plants on Juno IC. So blossoms had appeared a considerable period later on tho plants that wero left in tho light all day. These plants required a short day and a long night for flowering and seed ■bearing. In testa ' with other plants inst the opposite was found to be true. Tho plants that were left in the-lirilt all day did not grow luxuriantly, but produced flowors and seed, while those that" were kept in the dark a part of tho day made abundant growth but produced no seed, or else were greatly retarded in producing seed. According to Mr. Garner, temperature, except perhaps excessive hent or eold, appeared to oxert no influence in these tests. The results wero the same, even when the-temperature was higher in iho dark house than on tho outside. Another striking illustration of the relative unimportance of teinnernture was tho fact that plants kept in the dark for a part of the day underwent, in rihsunimor. the changes that in Nature conio in tho fall, and have always been attributed to lower temperatures. This nko wns true, he said, even whon the dark-houses registered a higher temperature than the outside summer temperature.

It is expected llint tho influence of this discovery will bo of vital importnnco on crop yields. Certnln crops in the fruiting of which it was always believed temperature was the chief "factor may now he speeded up in production. As in tho card of violets, oranges, bananas, (rrnpofrnit, and what not may soon ho dissociated from certain temperature sections of the country. But the main thine is that there will, apparently, ho greater production and eventually a reduction in tlio price.— "New York Evening Post."