September r, 1882.] THE TROPICAL AGRICULTURIST. 



269 



lying ou the surface The results were, therefore of no 

 value, except to iujicato certain percautions necessary to 

 secure scientific facts, and need not be here given. 



First Sekies. 

 Garden soil, ground coprolite, dissolved coprolite (super- 

 phosphate), and guano were then taken, and all sun-dried, 

 though not completely. Small stoneware jars, all of the 

 same size and shape, were than filled with as nearly the 

 same degree of compactness as could be attained. They 

 were then set upon a platform in a tray containing water, 

 and the whole enclosed with a large glass bell to confine 

 the evaporation. Weighings were made every day, but as 

 they harmonised throughout only as many are given as 

 to show the general re.sults. From May 28 to .lune 8 the 

 earth lost 25 parts from 1,000, the gi'ouud coprolite gained 

 14 parts, the dissolved coprolite gained 39 parts, and the 

 guano gained 80 parts. Undoubtedly had the jar of earth 

 stood in the water-closed bell alone it would have gained 

 wieght, but the absorptive power of the dissolved coprolite 

 and guano immediately beside it caused a still further dry- 

 ing of the less absorptive soil; and this result shows that 

 such manures in a comparatively tlry soil wall attract to- 

 wards their particles the moisture in the surrounding soil, 

 and therefore become more rapidly liquified and available 

 for roots. 



Second Semes. 



But the conditions under a glass bell were somewhat 

 artificial. I next thoroughly sun-dried quantities of earth, 

 cow-dung (pulverised), ground coprolite, dissolved coprolite, 

 potato manure, and guano. They wore all in a state of 

 fine division. Oups and pans corresponding with each other 

 in size and surface were fiUed with the various manures, 

 and the surface .struck off with a straight-edge. It would 

 have been possible to have put the same weight into the 

 competing jars, but this would have neceissitated different 

 degrees of compression, and it was therefore resolved to 

 compare equal bulks exposed with equal surfaces. The 

 cups were of different sizes, the same numbers (1,2,3) in 

 the table being of the same size. The whole were placed 

 in a large tray aud set in the floor of a disused milk-house. 



Between June 3 and 10 the earth had gained in each 

 cup 2 per cent, the cow-dung 10 per cent, the ground 

 coprolite 3 per cent, the dissolved coprolite 6, 7, and 8 

 per cent, in the respective cups; the Potato manure 26 

 per cent in one cup and 35 per cent in the other, and 

 the guano had gained in one cup 10 per cent in another 

 15, and in the third 19 per cent. The gain is greatest 

 in some of the small pans, simply because the absorbing sur- 

 face exposed to the air bears a greater proportion to the 

 weight of manure in the pan in the smaller pans than 

 in the larger. Where there is little absorptive force the 

 difference is small. 



It is seen from the figures that the earth has less 

 absorbing power for atmospheric moisture than any of 

 the manures compared with it. The next lowest in this 

 power is the groimd coprolite, then follows the dissolved 

 coprolite, absorbing twice as much moisture as the ground 

 coprolite; then comes the cow-dung or farmyard manure, 

 absorbing rather more than the dissolved coprolite; next 

 follows the guano, with a still higher absorptive power; 

 and lastly comes the Potato manure, taking in form the 

 air nearly four times as much water as the superphosphate. 



These results arc not at all meant to give absolute 

 factors of hygrosorptive power, but merely to show that 

 this power varies greatly in different manures. For per- 

 manent comparisons probably a standard cup would have 

 to be adopted with various other fixed conditions ; but 

 into this point I need not here enter. 

 Thibd Seeies. 



The manures for the third series of comparisons were 

 completely sun-dried and pulverised, and turned over in 

 a current of air under bright sunshine till all the moisture 

 which could be driven off in this way was got clear of. 

 The p.ans were then loosely filled, and the surfaces evenly 

 struck off. For each kind of manure there were two .pans 

 of different sizes; all the No. 1 pans being largest and of the 

 same size, and all the No. 2 pans being also equal to each 

 other. They were then placed in a tray ancl set in the 

 floor of an outhouse. Tlie door and window permitted 

 a constant current of air over the pans; but they were 



completely protected from all rain. They were exposed 

 from June 13 till July 30, and were weighed sixteen times. 

 The weights of dry manure are made 100, and the increase 

 in each case is reduced and stated percentively as before. 



Notes were kept of the state of the weather, which 

 was sometimes dry and sometimes wet, but not much rain 

 fell during the time under notice, so that the air was in 

 an average state of saturation. It was not thought fit to 

 continue the experiment longer, because large crops of mould 

 began to show themselves on some of the pans, especially 

 those containing the Turnip and Potato manures ; and , as 

 many fungi have a .strong affinity for moisture, further 

 results would have been vitiated. 



The manures are placed in the table in the order of 

 their absorptive power, and it will be seen that the soil 

 has absorbed 3 per cent, the ground coprolite 5, the cow-duu ■ 

 16, the dissolved coprolite 25, the Challenge manure 37* 

 the Turnip manure 39, the guano 53, and the Potato manure 

 92 per cent. The earth, under the conditions of atmosphere 

 which here affected the experiment absorbed in a few days 

 all the moisture it was capable of withdrawing from the 

 air, and the ground coprolite behaved in a nearly similar 

 manner. The cow-dung after July 15 gave off a "little of 

 the water it had up to that date absorbed. The super- 

 phosphate continued absorbing at a diminishing rate up 

 to the end. The Challenge manure, Turnip rhanure, guano 

 and Potato manure, .also went on to the end adding to' 

 their water, at a rate, upon the whole, garduaUy dimim'sh- 

 ing, the guano having added about one-half to its weight 

 and the Potato manure having nearly doubled its weight! 

 — Gardeners' Chronicle. 



EXPEEIIMENTS WITH THE ELECTRIC LIGHT. 



It is really a matter of the greatest importance in 

 vegetable physiology to ascertain precisely what is the 

 effect of growing a plant under continuous Ught. The 

 prevalent notion among physiologists is that light retards 

 gi-owth — that a plant feeds by day by virtue of the sun- 

 light, and uses up at night the food so gained, or rather 

 that which lias previously been so gaineil and stored in 

 the tissues. At first sight it seems as if this opinion must 

 be in direct contradiction to facts that come under our 

 daily observation— that it must be directly contrary to 

 what is observed in the short summers but nightless days 

 of the far North, where for a few weeks the plants are 

 constantly exposed to light, and where, in consequence 

 growth are harvest operations occupy a much shorter 

 time than with us. It would seem also that the results 

 already obtamed by the aid of the electric hght are directly 

 contradictory to the opinion of the physiologists. But 

 the divergence is not so great as it appears. Laboratory 

 experiments are one thing, ordinary cultural experiments 

 are quite another. It is the object in the laboratory, as 

 far as possible, to study the influence on plants of licrht 

 only, or of heat only, or of moisture only, to isolate each 



factor of a plant's growth, and study it by itself see 



what it does, and what it does not do when separated 

 from other agencies. In Nature, or under ordinary cultiv- 

 ation it is quite another matter. All the forces of Nature 

 come into play, and fashion the plant by their combined 

 influence. The action of light is controlled by that of 

 heat and moistm'e, and so the plant is the result of the 

 concurrent operation of many forces, aud it varies in 

 character and in the way it does its work according as 

 it is equally or unequally influenced by these ao-encies. 

 It is rash at present to speculate, still more so to dog- 

 matise, as to the absolute necessity for rest in plant- 

 growth — we know how desirable it is sometimes — rash to 

 affu'in that periods of darkness are absolutely essential to 

 their health. On all these points we want accurate in- 

 formation, and should welcome it from any source. For 

 immediate practical purposes we need not, however, be so 

 exacting It is for early forcing purposes, as we' have 

 before said, that we imagine the light will be found most 

 useful. It is now established suflicieutly that the light, 

 properly applied, will supplement the dayhght and afford 

 light when the sun does not, and that in so far it will 

 hasten vegetation and promote tlie more rapid rijieniug 

 of fruits. But whether it will do so at such a cost as 

 to allow of commercial success is a point that has not 

 yet been satisfactorily a.-asvietei.— Gardeners' Chronicle. 



