Vol. XIII. No. 326. 



THE AGRICULTURAL NEWS. 



:m 



STUDENTS' CORNER. 



DYNAMICS OF A PLOUGH. 

 Takt I\'. 



In preceding nuinl)er.s extracts from the article utulei' 

 review* have been given in e.xtenso. In thi.s number an 

 abstract of the concluding paragraphs is presented. 



Two hor.ses yoked abreast, i.e. two equal parallel forces 

 give a resultant equal to a single force acting midway 

 V)etween them of etiual magnitude to their sum; in other 

 words, tjie two horses abreast have the same re.sult as one big 

 horse twice their power, yoked midway. (See fig. 12.) 



To draw tlie plough straight forward, the force must 

 take a straight line from a pf)int midway between the hame- 

 hooks of the single large horse. The liricle-pin must be on 

 this imaginary straight IJTie. 



If instead of two iiorses abrea-st, four horses are yoked, 

 two in front of two, a new vortical resultant has to be formed 

 a.s seen in fig. l.'i. 



Ki.;. 12. 



This resultant gives a combination half-way between the 

 front and back hor.ses. The bridle-pin must be lowered 

 about 2 inches from the proper position for two hor.ses. In 

 the case of three horses aliroast the resultant is shifted to the 

 middle of the niiddle horse at his hame-hooks. The bridle- 

 pin must be shifted 6 inches or 7 inches on the bridle. As 

 to the horizontal position of the bridle-pin, four horses, two 

 in front of two, have the same effect as two hor.ses abreast, 

 and six hor.ses, three in front of three, the same effect as three 

 horses abreast. 



NOT EX0U(iH DIP. See to the .share: if it is worn liovel- 

 led on the underside and is of steel, get it sharpened by 

 a blacksmith: but if it is of cast iron, grind it bevelled on 

 the upper surface or put on a new one. Cast .shares arc 

 made by all makers with different amounts of dip, and can 

 be got by ordering when required with more or less dip. 

 If the .share is in good order and nir.re dip is still wanted, 

 raise the bridle and shift the coulter — if this be circular — 

 farther back. This is veiy necessary if the ground is hard 

 on the surface, as a circular coulter, more especiajly when 

 blunt, then becomes a wheel to hold the plough up out of 

 the ground. Circular coulter-blades should- always be ground 

 sharp when worn blunt, but this is seldom done. In vwy 

 hard or stony land, straight-bar coulters should hi' usi'd 

 instead of circulars. 



TOO MUCH DIP. Lower the bridle and shift the coulter. 

 If it is circular forward, put (jn a share with less dip. 



TOO MUCH L.VSD. Shift the bridle-pin to the left, set 

 the coulter to run oft" land, a!id shorten the couplings of the 

 land horses. 



NOT ENouoH L.\XD. Shift the bridle-pin to the right 

 and set the coulter to point more to the left. If it is a circidar 

 c'oulter and worn off land, get it ground, bevelling on the 

 right-hand side to a sharp edge, and put in the .shank with 

 the flat side to the left. Set the land- wheel to point to the 

 left Ijy packing it behind the square-holed washer — a short 

 piece of fencing wire will do. Bend the steering-rod just 

 behind the knuckle-joint, to make the wheel run pointing 

 more to the left. See that the share is not worn Ijevelled on 

 the underside. A share so worn, reduces the land by making 

 the plough run lighter on the wheels. The wheels are all set 

 to run slightly to the left, and if the pressure upon them is 

 reduced, they lo.se their grip on the surface, and hence also 

 their guiding effect. Widen the land horse's couplings and 

 keep them farther to the left. ; 



In conclusion a share should be 2 inches or 3 inches 

 narrower than the furrow which is to lie ploughed. It is 

 a mistake to use a share too Avide. The idea that the 

 draught of a plough is proportionate to its weight, is also 

 a mistake. The draught of every plougli will vary with the 

 width and depth of the furrow, and the condition and quality 

 of the land. A\Tiilst a light plough is easier to handle for 

 a man, it makes hardly any rlifference to the hor.ses, within 

 reasonable limits. 



Fi.;. 13. 



Such are the theoretical principles governing the appli- 

 cation of power to draw jjloughs, and thej- hold good under 

 all circtimstances. It must be remembered that the position 

 of the resultant centre of resistance varies under different 

 circumstances. Practical ploughmanship consists largely in 

 knowing what to do to adjust the resultant force of the team. 

 The following are a few hints of what to do under ordinary 

 difficulties. 



1914. 



* The Journal of Agti<:nlbi,re of New Zealand fur .June 



Stomata and Leaf Movement.— It has been 



recorded in a recent issue oi the Wrs( Indian Bulletin that 

 the number of stomata, per unit of area, varies in a constant 

 manner in different varieties of sugar-cane, and that these 

 variations are correlated with certain variations of leaf 

 structure. In connexion with this subject of the location of 

 stomata on growing seedlings of other Cramine;e, the 

 Gardeners Chronicle for September 12, 1914, records .some 

 observations of interest. In wheat and oats, the stomata 

 occur in the greatest number at the apex of the cotyledon, 

 which is the part that moves most readily to stimulation 

 from light, while at the base there is an absence of stomata. 

 In seedlings of Paiiicum and Paspalnm, the .stomata are 

 evenly distributed over the whole surface, and in these the 

 whole cotyledon is equally infinenced by light through 

 its length. It would seeem, therefore, that there is 

 a connexion between the distrilmtion of stomata, and the 

 perception of light in seedlings; and ]ii>ihaps in more mature 

 leaves. 



