Vol. XVII. No. 424. 



THE AGRICULTURAL NEWS. 



237 



THE EFFECTS OF ULTRA-VIOLET RAYS 

 ON PLANTS. 



As is well known, in the spectrum of sunlight there 

 are seven visible colours, red, orange, yellow, green, blue, 

 indigo, violet, which are visible to the human eye, but besides 

 these, on each side of the spectrum there are invisible rays 

 known on the one side as ultra red, which are heat rays, and 

 on the other side ultra-violet, which are chemically active. 

 These ultraviolet rays vibrate so many million times a second 

 that our eyes are blind to them, just as our ears are deaf to 

 the most rapid vibrations of sound. But these invisible 

 rays which are recorded on photographic plates have a strong 

 chemical effect on plants. They are very quickly absorbed 

 by the atmosphere^ and only a comparatively small part of 

 these rays given off by the sun reaches the earth's surface. 

 An interesting paper by Taizan Tsuji, in the Louisiana 

 Planter, .June 29, 1918, records some experiments made by 

 him on the stimulating effect on the ultra-violet rays on 

 some tropical crops. 



In one experiment, germinated sugar-canes were planted 

 in moist soil, and cultivated in the dark at a temperature of 

 about 22 C. The plants grew, but naturally turned pale. 

 After thirty days these etiolated plants were divided into 

 two groups, one of which was exposed to sunlight, while the 

 second was exposed to the ultra-violet rays produced by 

 a quartz mercury-vapour lamp. After two hours and a half 

 the etiolated leaves of the sugar-cane exposed to the action 

 of the ultra-violet rays were found to take a deep green 

 colouration, whereas those exposed only to sunlight still 

 preserved their yellow appearance. 



In another experiment three rows of sugar-cane were 

 planted: the first row was shaded with coloured glass so that 

 the ultra-violet rays of the sunlight were decreased by 

 .50 per cent.; the second row was planted in open sunlight so 

 as 10 obtain all the ultra-violet rays naturally existing in 

 the rays of the sun; the third row was planted so as to be 

 fully exposed not only to the sunlight but to ultra- 

 violet rays from the mercury lamp for a certain time 

 each day. All of these rows received the same amount 

 of fertilizers. After several months the result was 

 that, in the first row the sugar-canes gained l|Tb. each, 

 on an average; the canes in the second row gained 2* lb. 

 on an average; while those in the third row gained 3^ ft), 

 average. The writer of the article thinks that there- is a 

 possibility of a future use of these rays in sugarcane cultiva- 

 tion in Hawaii, where the experiments have been made, for, 

 as he points out, the row of canes in the above experiment, 

 exposed not only to the sunlight but to the ultra-violet rays 

 of the sun, had considerably more sugar than the canes 

 exposed to sunlight alone. 



In another experiment, unripe pine-apples exposed to 

 weak ultra-violet rays were found to ripen earlier than those 

 under sunlight. Two rows of pineapples were planted in an 

 open field, the first row of which was exposed to sunlight 

 only, while the second row, in addition to sunlight, was 

 exposed to the ultra-violet rays of the raecury vapour lamp 

 for forty minutes every morning. The result showed that 

 the pine-apples in the second row ripened earlier, and were 

 sweeter, larger, and more juicy than those in the first row. 



An experiment made on etiolated banana leaves showed 

 that after three hours action of ultra-violet rays the leaves 

 began to take on a marked green colouration, while five hours 

 sufficed to make their colour a deep green. Banana leaves 

 and stalks exposed to ultra-violet rays after having been cut 

 and kept in water were found two weeks afterwards to be 

 quite fresh, whereas some kept in diffused daylight were 



almost completely withered after six or seven days. The 

 writer thinks that by the use of these rays bananas may be 

 ripened and sent unspoilt to distant markets. 



The problem is to find a process by which these rays 

 may be obtained cheaply. They may be produced abundantly 

 by specially constructed mercury arc lamps with quartz sides, 

 but the cost at present of such an installation to stimulate 

 the growth of crops is commercially prohibitive. 



THE TWO SPECIES OF CABBAGE 

 PALM. 



As some confusion exists whether the names 'royal palm 

 and cabbage palm are only local appellations of the same 

 tree, or whether they are really two species, the following 

 note will be useful in clearing up the question. 



According to Dr. Beccari, the well-known Italian 

 authority on palms, there are two if not three species of 

 Oreodoxa to which the name cabbage palm or royal palm is 

 given in the British West Indies. In a monograph on the 

 palms indigenous to Cuba, published in the Fomona College 

 Journal of Economic Bofany, Vol. II, No. 2, Dr. Beccari 

 gives descriptions of these three species. 



In the first place, Oreodoxa regia, the royal palm, is the 

 species commonly found growing in the Greater Antilles — 

 (Juba, Jamaica, Santo Domingo, and Porto Rico — and also in 

 St. Croix. In this species the stem is usually more or less 

 fusiform, bulging out sometimes in more than one place, 

 giving the impression that the palm has been influenced 

 during its growth by periods of uaecj'ial nutrition. It is 

 true, however, that some individuals have stems almost 

 regularly cylindrical from base nearly to summit. The leafl- 

 ets in this species are alternately inserted in contrary ways 

 along the midrib, and stand in four different planes, at least 

 in its lower and intermediate parts, but are more regularly 

 set, almost on one plane, towards the end. The fruit 

 in this species is almost globose, the breadth being only little 

 less than the length. The stamens of the male flowers are 

 about as long as the petals when they open, and they 

 remain fairly upright, between these latter. 



A second species {O. charil>aea), which occurs in Porto 

 Rico, differs so slightly from O. regia as to be considered by 

 Dr. Beccari as only a geographical form of the latter, or in 

 any case nothing more than a second degree species. 



The common cabbage palm of the Lesser Antilles, and 

 apparently of Trinidad also, which is stated to be peculiar to 

 those islands, is O. olcracea. The stem of this species is 

 quite cylindrical and never bulging, being always thickest at 

 the base. The leaflets in this species are equidistant, and all 

 on one plane, especially in the intermediate portion of 

 the midrib. Its fruit also differs from that of O. regia, in 

 being rather elongate than globose, and being somewhat 

 curved and concave on the side of the stigmas. The male 

 flowers, too, are quite different in appearance from those of 

 O. regia, as the stamens spring beyond the corolla a long 

 time before the anther cells open, and are much longer than 

 the petals, above which they lie almost horizontally. On 

 account of this circumstance, the inflorescence of O. oleracea 

 has quite a different appearance from that of O. regia. The 

 white floury matter which covers the inflorescence of both 

 palms when still enveloped in the spathes, and which is 

 dispersed when the spathes open, is much more abundant 

 in O. oleracca- 



On account of its beautifully cylindrical stems, O. olc- 

 racea would seem to be superior to O. regia as an ornamental 

 plant, in spite of the latter s royal designation. 



