6oo 



THE TROPICAL AGRICULTURIST. 



[February 2, 1885. 



Why, one may ask. is dew less needed in the hot months 

 of summer than in the spring or autumn? For au obvious 

 reason. As the season advances, the roots are striking 

 down deeper and deeper every day. In summer they are 

 six, ten, fourteen or even twenty inches or more below 

 the surface, where it is always comparatively moist. Bain 

 may not fall for weeks, yet they are getting moisture from 

 below all the time; but when plants have just completed 

 germination, and when their roots are near the surface, 

 a drought of a few days would be fatal but for the nightly 

 deposits of dew. 



It may be asked again what is the necessity of the 

 heavy dews in the early fall, when the crops are gathered 

 and housed? Precisely the same as in the early spring. 

 In the early fall, the seeds are sown which are to fructify 

 the next year. Wheat and oats, rye, turnips, the grasses, 

 etc., need the autumnal, as the already ripened crops need 

 the vernal, dews. 



To another point I will call attention. To get copious 

 deposits of dew, plants must be chilled; but if chilled too 

 much, the dew is frozen into frosts, and vegetable vitality 

 is destroyed. To secure a benefit, a danger is incurred; 

 but in the very process of securing the benefit, the danger 

 is weakened. Vapor is water with so much heat in it — 

 heat in the latent state. When water boils, no matter 

 how much heat we add, we neither make it nor the escaping 

 vapor any hotter. Both have the common temperature of 

 212 degrees. All the excess of heat we add is simply 

 employed in causing the liquid water to take on the gaseous 

 form of vapor. Now when we condense this vapor, the 

 heat, before latent, is evolved or given out. When aqueous 

 vapor is in the process of condensation into dew, all its 

 latent heat — that heat which made it vapor — is evolved 

 on the surface where the condensation takes place. Consider 

 a fine tobacco field, the broad leaves ripening in the mild 

 September. The leaves lose heat rapidly by radiation, they 

 become chilled, the aqueous vapor is condensed into dew, 

 but in the act its latent beat is evolved, and so warms 

 up the leaves, and thus diminishes the liability to injury 

 from frost. The atmosphere immediately brooding over 

 the leaves is sensibly warmer than the atmosphere elsewhere. 

 If the same amount of water be sprinkled at night-fall 

 upon the leaves, the cold may be sufficient to freeze it; 

 but not sufficient if this water has been condensed from 

 vapor, for the process of condensation throws out, in 

 sensible form, the latent heat of the vapor. 



The process of aqueous condensation, or dew formation, 

 postpones the appearance of frost. Plants must become 

 chilled to form dew, but, in the condensation of aqueous 

 vapor, heat is thrown out to prevent frost. This battle 

 goes on for weeks, until at last the increasing length and 

 coldness of the nights get the advantage. The cold is too 

 great to be counterblanced by the heat evolved from 

 aqueous condensation, the dew freezes as it forms, and the 

 plant is killed. 



We have shown the necessity of dew in the early fall 

 to the crops that are seeded then, which are to live and 

 grow through the winter and mature in the next summer. 

 But some crops, already ripening, as tobacco, are remarkably 

 benefited by the early autumnal dews. Little rain and 

 copious dews in the early fall make tobacco leaves thick, 

 heavy and oily. Alike, its weight is increased and its quality 

 improved by comparatively dry weather and heavy dews. 

 Dew then, to some extent, has a double function, furnishing 

 to all plants, in the earliest stage of their growth, small 

 but frequent supplies of water, when the supply from the 

 soil is liable to be scant, and enabling others, notably 

 tobacco, to attain, while approaching maturity, their highest 

 perfection. — American Farmer. 



Vanilla Beans. — These are the fruits of an orchid, — 

 Vanilla plauifolia, a native of Mexico, but which extends 

 north to the borders of the United States. Though the 

 writer has seen it under culture for nearly half a century, he 

 does not remember ever seeing a seed vessel produced under 

 these circumstances. Most orchids only seed when under the 

 attentions of insects, and perhaps this is why it } ields its 

 "beans" or seed vessels so freely in a wild state. The island 

 of Tahite sends out about 2,000 or 3,000 pounds annually.— 

 Gardeners' Monthly. 



Cassia Occidentalis. — The seed of this plant, which is 

 occasionally found in the Southern States, contain no 

 caffeine, nor any other alkaloid, but some fatty oil which 

 easily becomes disengaged and empyreumatic upon applic- 

 ation of heat to the seeds, in a partially closed vessel. The 

 parching or toasting of the seeds causes volatilization of 

 water contained therein ; then the oily substance makes its 

 appearance on the walls of the container, accompanied by an 

 odor closely resembling that of parched beans or peas, very 

 remotely, and with some imagination only, simulating that 

 of coffee. Treatment of the parched seeds with dilute 

 alcohol, as also the turbid, brown watery extract, developed 

 the presence of phosphates of lime, potash, and soda. — 

 Independent Joui*nal. 



The Amount of Water Absorbed by Trees. — In the 

 official report of the Geological Survey of Wisconsin is an 

 account of the determinations made by Dr. J. M. Anders of 

 the amount of water pumped from the earth by trees. He 

 finds that the average exhalation from soft thin-leaved 

 plants in clear weather amounts to about 1 J ounce Troy, per 

 day of twelve hours, for every square foot of surface. Hence 

 a moderate-sized elm raises and throws off 7J tons of water 

 per day. In the report the facts are applied to what is going 

 on in America, where certain inland fertile districts are be- 

 coming converted into deserts by wholesale clearings ; and 

 in other places, such as the plains of Colorado, where only 

 five or six years of irrigation and planting have already pro- 

 duced a measurable increase of rainfall. It is maintained that 

 the deserts of Syria and Africa are the results of cutting 

 down trees, and that original luxuriance may be restored by 

 skilful replanting. — Timber Trades Gazette. 



Pearl Fisheries of Persia. — The pearl fisheries appear 

 to be in a languishing condition. Formerly a very large source 

 of revenue, they are at the present day probably not worth 

 to the Government more than 50,000 tomans or £16,000 per 

 annum. The pearl beds are farmed by the chief men of the 

 adjacent towns, and, instead of being distributed in Persia, 

 are for the most part sent to Europe by. the steamers plying 

 to the Persian Gulf. The reason for the present condition of 

 the Persian pearl beds is that they have been allowed no rest, 

 but have been constantly worked. In Ceylon, the pearl 

 oysters are allowed a rest for intervals of two years, during 

 which they are allowed to mature. Mr. Benjamin says there 

 is reason to believe, however, that the beds at the island of 

 Kanik, near Bushire, which have not been worked for some 

 time, are now in a condition to repay capital expended there, 

 especially if diving is extended to a depth uf fifty to sixty 

 fathoms. As the ordinary depth reached by pearl divers is 

 rather less than this, the Persian Government have recently 

 sent to England for diving dresses of the latest invention, 

 and an experienced diver has been engaged at a high salary. 

 With the assistance of these, it is expected that the pearl 

 fisheries of Persia will regain their former importance.— 

 Journal of the Society of Arts. 



Injurious Insects.— The first injurious insect competition 

 ever held took place at Frome in England recently. Miss E. 

 A. Ormerod, F.M.S., the consulting entomologist to the 

 Royal Agricultural Society of England, offered prizes of £3, 

 £2 and £1 for the best collection of specimens of food plant 

 injured by insects, accompanied by samples of the insects 

 injuring them, by a short written account of the insect 

 attack, and of the methods of remedy or prevention adopted. 

 Only one exhibit turned up, and this was judged by Mr. 

 Henry F. Moore, who awarded it the first prize. It was sent 

 by Mr. Herbert Haley, of Feltham Cottage, Frome, and was 

 a most instructive and picturesque arrangement. The speci- 

 mens included plum, geranium andred currant leaves attack- 

 ed by caterpilars, potatoes and spinach by wireworms, turnips 

 by turnip fly, celery by, grub, strawberry by chrysalis of 

 caterpillar, potato by Colorado beetle, branches of gooseberry 

 tree stripped by saw-fly, cabbage leaves by butterfly, onion 

 by maggot, filbert tree by various insects, stephanotis by 

 mealy-bug, centipede, daddy longlegs, earwigs, &c. Each 

 insect was shown in a separate bottle, and there was a short 

 account of the insect attack, and of the methods of remedy 

 or prevention adopted. The specimens were also accom- 

 panied by colored drawings of the insects, life size or 

 greatly magnified. It is greatly to be regretted that only 

 one entry was received, but the interesting nalrue of the 

 exhibit will be certain to cause it to be repeated in other 

 places. — Australasian. 



