2IO 



HARDWICKES SCIENCE-GOSSIP. 



which is the first substance formed in the leaves of 

 plants, and is, as it were, the raw material from 

 which the other constituents of the plant are elabo- 

 rated. The ashes of plants, especially those of root- 

 crops, consequently contain potash to a considerable 

 degree. Thus in those of wheat there is about 17, of 

 barley 23, of meadow-hay 25, of turnips 41, and of 

 potatoes 45 per cent. Potash may be applied as 

 manure in the form of potassium-salts, kainit, wood- 

 ashes, seaweed or urine. 



Iron has been found necessary for the formation of 

 chlorophyll, the green colouring matter; of plants, 

 and hence of starch, which is only formed in those 

 cells containing the chlorophyll granules. There is, 

 however, already sufficient iron in the soil, and most 

 manures contain a little. 



Lime and Magnesia are essential to plant growth, 

 but their functions within the plant are not thoroughly 

 understood. The former acts physically and chemi- 

 cally in the soil in improving its texture, accelerating 

 the decomposition of organic matter and silicates, 

 and in combining with the nitric acid set free 

 during nitrification. Indeed, it appears that this 

 process cannot be carried on unless some salifiable 

 base be present. The proportion of lime present in 

 the ashes of plants varies greatly ; those of wheat 

 and barley containing about 5, of meadow-hay 16, of 

 turnips 20, and of potatoes 15 per cent. Magnesia 

 constitutes a very much smaller percentage. Lime 

 manures are quick-lime, chalk, marl, super-phos- 

 phates, gypsum, building-rubbish, etc. 



Chlorine has only been found essential to plant- 

 growth in the case of buck-wheat, but most plants 

 contain a trace. This is partly derived from the 

 atmosphere, the average amount annually contributed 

 by the rain at Rothamsted being 14*92 lbs. per acre, 

 which is equivalent to 24*59 lbs. of common salt. 

 If applied as manure it is generally in the form of 

 common salt, but most manures contain sufficient 

 chlorine for practical purposes. 



Soda is not necessary for plant-life, and is only 

 found in very small quantities in the ashes of plants. 

 It probably acts chemically in the soil as a base, as 

 in the case of lime. It may be applied as to sodium- 

 salts, urine, soda- felspar, etc. 



Sulphur is another of the constituents of proto- 

 plasm, but is seldom applied as manure, as soils 

 contain sufficient in combination as sulphates. Rain, 

 too, contains a trace of sulphuric acid, the average 

 annual amount at Rothamsted being iS"5 lbs. per 

 acre. There is more sulphur in turnips than in any 

 other root-crop, and," therefore, super-phosphates, 

 which contain much gypsum and often free sulphuric 

 acid, are used to manure them. 



Silica is found in the ashes of all plants, although 

 not essential to plant-life. It occurs chiefly in the 

 stem of most of the Graminaceae, and often in large 

 quantities. Thus the sugar-cane contains so much as 

 to render the entire abstraction of sugar by pressure 



practically impossible, and the resulting " megass," 

 or crushed canes, useless for fuel. The ashes of 

 the straw of wheat, barley and oats, contain about 

 68, 51 and 47 per cent, respectively. Messrs. Lawes 

 & Gilbert, however, have found that wheat can be 

 grown entirely free from silica, and yet of as good 

 quality. Most manures contain it, but, owing to its 

 abundance in soils, there is no need for it to be 

 specially added. 



(To be continued.) 



ASTRONOMY. 

 By John Browning, F.R.A.S. 



AT the last meeting of the Royal Astronomical 

 Society, a paper by Mr. Williams was read on 

 a coming conjunction of a remarkable dark spot on 

 Jupiter with the red spot. The great red spot has now 

 been closely observed for about twelve years, but very 

 little is known of its attitude relatively to the other 

 markings on the planet. A large dark spot has now 

 been visible for some time on the southern belt, and 

 this is now gaining on the red spot rapidly. 



Mr. Williams considered that if the black spot 

 remained visible and continued its motion from east 

 to west, it would overtake and pass the red spot, 

 and this would afford an opportunity of observing 

 whether it passes over the red spot or if it is covered 

 by it. He calculates that the black spot will be in 

 conjunction with the following end of the red spot on 

 the 29th July, with the centre on the 28th of August, 

 and with the preceding end on the 27 th of September ; 



Rising, Southing, and Setting of the Principal Planets, 

 at intervals of Seven Days, for September. 



