Nov. 2, 1885.] 



THE TROPICAL AGRICULTURIST. 



335 



Destroying Weeds on Walks (/. C, Cheshire).— &. 

 short time ago several methofls were described in 

 the JourDal of destroying weeds on walk-f. Salt is 

 only objectionable by making some walks too moist. 

 In the case of dry walks and positions this objection 

 vanishes, and applied in dry weatlier salt is effective. 

 Arsenical solutions will kill weeds. Boil 1 lb. of 

 powdered arsenic and 2 lb. crushed soda, then dilute 

 with seven gallons of water. Add one part of common 

 vitriol to thirty parts of water, mix and apply. Mix 

 »n ounce of " crude carbolic acid to each gallon of 

 water prepared, and with this water the gravel. 

 Petrolum will kill weeds; the quantity to use you 

 can easily ascertain by experimeut. Whatever is used, 

 Box or Grass edgings must be protected.— /ocrna^ 

 of Bort culture. „, , 



The Sweet Potato. — The editor of the Vnarleston 

 News says he has always been of the opinion that 

 the great value of the sweet potato crop in the 

 Southern States was not duly appreciated and 

 suiliciently utilized. Eoot crops are always more 

 prolfic tliau grain crops. They exhaust land less and 

 give more in return for labor and manure. Of course 

 they are not as nutritious pound for pound, as grain, 

 but in great increase of niateiial they yield more 

 nutrition to a given quantity of land than any of 

 the cereals. [X. B. as regards Oeylon. — Ed.] Irish 

 potatoes, turnips, beets, carrots, both in Europe and 

 in our Northern States, are all justly prized as the 

 most valuable of farm crops. The sweet potato is 

 superi(n' to them all as food for man and beast. It 

 may be used for all the purpo.ses to which the others 

 are applied, and for many others besides. In the 

 first state, just out of the ground, it makes an 

 excellent substitute for arrowroot by grating the 

 pulp into water and allowing the starchy matter to 

 subside. As a vegetabe, it is a favorite on every 

 table, cooked in great variety of ways. As a desert 

 it makes a better pudding or pie than a pumpkin. It 

 is good food for a stock of all kinds^horses, cattle, 

 shrcp and hogs. We know an old planter once who 

 always raised an abundance of corn and other pro- 

 visions for his stock, but who was an enthusiasm 

 over the sweet potato crop, esiimating it, on the 

 vield returned from the labor be!-towed as of more value 

 "than any other food-producing crop. — Suuthern Planter. 

 Spores Floating is the Aik. — Those who are 

 puzzled to understand how poores of Hemileia xastatrir 

 gel into the stomata of coffee leaves may find some 

 help in the following statement quoted in a recent 

 lecture : — 



It was not till 1876 that the systematic ob- 

 servations of air-borne spores was commenced at 

 Mont Souris by Dr. Miquel. Taking the average of the 

 four years, 1S79-82, Dr. Miquel found that each litre of 

 air coiitainril from 12 to 1.5 spores, and that, in general, 

 they were slightly more abundant during hot years. Tlie 

 effects of season were well marked. Thus in 

 there were G'6 spores per litre of air ; in 

 16-7 ; in summer, 22-8 ; in autumn, 10 8. By 

 of a most ingenious registering aero- 

 Dr, Miquel has been enabled to observe the 

 fluctuations in the number of spores. This 

 fluctation is very great indeed, and the causes of it 

 are not always apparent. One fact seems to come 

 out clearly, viz., that a fall of rain has the effect 

 of partially clearing the air of spores for a time. 

 The causes of the hourly fluctuation are, according 

 to Miquel, mainly two, viz., remote and local. Let 

 us imagine a mass of air travelling from north to 

 south. Coming from regions of ice, and orginally 

 very pure, it strikes a continent, and the mass of 

 air which impinges on the soil makes almost a 

 clean sweep of floating spores, and largely enriches 

 itself at the expense, as it were, of the masses of 

 air following in its wake. Thus the richness in 

 spores dimijiishes as long as the air blows strictly 

 from one direction. Among local causes of variation 

 ■may be mentioned the neighbourhood of great 

 towns or other centres of spore productions. Again :-— 

 Spores of cryptogams are the most common of all orgauio 

 particles found in the air. 



winter 

 spring, 

 means 

 scope, 

 hourly 



WooDEiV Labels for Trees. — A correspondent 

 writes: — I don't know how they preserve the wooden 

 Labels used at the Botanical Gardens at Peradeniya, Ijut 

 here is a method which seems to have been attended 

 with success elsewhere : — The following method of 

 preserving wooden labels that arc to be used on 

 trees or in exposed places is recommended ;— Thoroughly 

 soak the pieces of wood in a strong solution of sulphate of 

 iron ; then lay them, after tliey nre dry, in lime water. 

 This causes the formation of sidphate of lime, a very 

 insoluble salt, in the wood. The rapid destruction 

 of the labels by the weather is thus prevented. 

 Bass mats, twine, and other substances used in tying 

 or covering up trees and plants, when treated in 

 the same manner, are similarly preserved. At a 

 recent meeting of the Horticultural Society in Berlin 

 wooden labels thus treated were shown, which had 

 been constantly exposed to the weather during two 

 years without being affected thereby. 



Destructive organisms in the air and their in- 

 fluence ON HUMAN HEALTH Were thus noticed in 

 Dr. Poore's lecture on climate and health before the 

 Society of Arts : — 



Seeing how omnipresent are the micrococci, bacteria, 

 and bacilli, of which we have been speaking, how 

 they infest the air, the soil, the water ; and seeing 

 again that it is an undoubted fact that the organ- 

 isms of disease may live and grow in suitable 

 putrescible liquids outside the human body, it is al- 

 most a matter of surprise that we are any of us 

 alive to discuss the question. From what we have 

 been saying, however, it appears that for the flourish- 

 ing of infective organisms three things are neces- 

 sary, in addition to the organism, viz., some degree 

 of warmth, a suitable condition of moisture, aud a 

 "soil" apt to grow the organism. It is when we 

 get the coincidence of all the conditions that we 

 get the disease in its marked form. The cold of 

 the Arctic winter seems to be sufficient to i>revent 

 putrefaction, and to prevent the spread of many of the 

 zymotic diseases. In tropical countries, where putre- 

 faction flourishes, zymotics flourish, and if we want 

 to enjoy health in hot countries we must exercise 

 tho greatest care and circumspection in dealing 

 with all putrescible matters, whether cxcremental or 

 otherwise ; finally, it is only unhealthy persous who 

 become a prey to parasites, and a healthy man is 

 probably more thana match for most of the so-called 

 patholosica'. organisms. 



Mr. Forbes' residence for three weeks in the Keel- 

 ing Islauds enabled him to note what changes had 

 occurred since Darwin's vi,=it nearly half-.a-century 

 earlier. These are very slight, aud seem incompatible 

 with the theory that any subsidence has taken place, 

 because the inner margin of some of the islands next 

 the lagoon are sometimes half-a-mile distant from the 

 outer edge, and the greatest cyclones do not carry 

 thi^ coral rlehris nearly so far. It is now generally ad- 

 mitted that the celebrated " subsidence theory " of 

 the formation of atolls aud barrier reefs is unsound 

 as .1 general explanation of the facts; yet it so fully 

 and plausibly explained all the details of coral struct- 

 ure known at the time, as to eummanvl universal 

 acceptance and unbounded admiration. We have hero 

 a remarkable instance of the danger of founding a 

 general explanation of widespread phenomena 011 an 

 assumed basis, for the fact of long-continued subsid- 

 ence, which was the very foundation of the whole 

 theory, was in most cases quite incapable of proof. 

 It is also now apparent that the theory was to some 

 extent inconsistent with the views as to oceanic islauds 

 which Darwin himself originated and which are now 

 ger.erally admitted to be sound. His great argument, 

 th:it no single oceanic island possessed ancient strati- 

 fied rocks or contained a single indigenous mammal, 

 was equally an argument against the view that the 

 widespread coral archipelagoes of the Pacific and 

 Indian Oceans were due to the subsidence of co-ex- 

 toisive tracts of land, since it is almost impossible 

 tlirit all the higher points of these submerged lauds, 

 spread over nearly half the surface of the globe, should 

 b« without exceptiou of volcanic origin,— ..VafKre. 



