Vol. XII. No. 282. 



THE AGKICULTUJtAL NEWS 



i>'i 



Another peculiarity of these tannin complexes, and one 

 that more directly concerns the subject r(f this article, if the 

 fiict that tannins are held more tenaciously by coag'ilable 

 substances, such as the white of ega when they are in 

 a s'ate of coagulation than when not. | It has been shown 

 that tannin in its relation with a coagulible substance in the 

 persimmon, analogous to the white of egg, acts in the same 

 way. This is known as the principle of c 'llnidal protection. 



> 



In considering the case of astringenj fruits like the date 

 and persimmons, which when ripe appear to be entirely 

 devcad of the astringent principle, tannin, it should be 

 remembered that such fruits contain quite as much tannin 

 when non astringent as before. The tannin is simply 

 protected. 



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The .\rabs have for many centuries practised the art of 

 rii'L-ning dates artificially. This consi.sts in exposing the 

 Vunches of unripe fruit to the vapours of vinegar, of which 

 the active agent appears to be the acetic acid. The same 

 effect can be produced by other chemicals and by supra- 

 normal temperatures. The cause of the change in some 

 instances i.s o.xidation which renders the tannin tasteless. In 

 the case of the action of acid vapour on the date, evidence 

 points conclusively to the non astringency being due to the 

 formation of a colloidal protector, and uot to the destruc- 

 tion of the tannin. 



As regards the artificial ripening of persimmons in 

 Japan, a custom is followed by which the unripe fruit is 

 stored in air-tight tubs in which the alcoholic beverage sake 

 has been kept The ripening may be due to the effect of 

 alcohol or a slight amount of acetic acid. E.xperiments 

 indicate that the alcohol stimulates increased respiration, 

 and that the carbonic acid gas produced is the ultimate 

 cause of the change. 



This has led to the question as to whether carbon 

 dioxide, under pressui-e, might not bring about a similar 

 change with greater rapidity. Fruit was placed in a specially 

 devised but simple apparatus composed of a piece of -t-inch 

 gas pipe suitably capped and supplied with a pressure gauge 

 and with the outlets guarded by gas cocks. The effect on 

 the fruit of different pressures of carboa dioxide was tried, 

 and it was found that fruit exposed to^ pressure of 1.") lb. 

 to the square inch become non-astringent in about thirty six 

 hours, whilst that subjected to 4-5 D). pressure became 

 non astringent in about fifteen hours. 



To explain tliis change it is necessary to return to the 

 principle of colloidal protection. Tannin oscurs in the date 

 fruit in little sacs. Along with the tannin in the.'^e sacs is 

 a mucilaginous substance which becomes coagulated in the 

 presence of acids and thus forms a colloidal protection, 

 holding in the tannin so that it may n<it escape except at 

 a very slow rate — too .slowly for it to be detected even by 

 the delicate membranes of the mouth. .Although a colloid, 

 tannin is not a coagulable one, like gum and mucilage; but, 

 as already pointed out, it possesses those peculiar properties 

 of combining loosely with coagulable substances and of being 

 held tenaciously by them when coagulated. In a word, the 

 tannin masses of the ri/ie fruit are a sort of vegetable leather, 

 which like ordinary leather gives up it3 tannin only very 

 slowly. The action of the carbonic acid is of course to coagu- 

 late the mucilaginous substance, and this effect may be 

 compared with the recent discovery that carbon dioxide can 

 cause the coagulation of the latex of rubber trees. 



WEEDS AND M.MZE CULTIVATION. 



A bulletin (No. 257) was issued toward the end of 

 last year, by the Burcaii of Plant Industry of the 

 I'^nited States Department, of Agriculture, which gives 

 the results of invescigatii>ns designed to di.scover how 

 far the beneficial etiCects that follow cultivation in 

 maize fields is due to the removal of weeds. In the 

 experiments, plots cultivated in the ordinaiy way were 

 compared with those in which the weeds were simply 

 removed with a sharp hoe, with as little disturbance of 

 the soil as possible. Under the conditions of the 

 experiments, almost as good results were obtained by 

 the simple removal of the weeds as by ordinary cultiva- 

 tion; in fact, in some cases, the latter seemed to 

 'cultivate' the weeds as much as the crop, for at the end 

 of the season the simply-weeded plots were cleaner 

 than the cultivated. More work is required before the 

 results can be accepted in a general way. For the 

 preseiit, it is sufficient to (ietail the conclusions as they 

 are expressed in a satnniary at the end of the bulletin: — • 



A number of tests made at several agricultural experi- 

 ment stations seem to indicate that it is the weed factor that 

 makes the cultivation of corn necessary, or, stating the 

 proposition conversely, that cultivation is not beneficial to the 

 corn plant except in so far as removing the weeds is concerned. 



The sul'ject of weed control is recognized as a fundamental 

 one in tillage philosophy, ft was therefore determined to carry 

 on, over a wide range of climatic and soil conditions, a large 

 number of tests of the relative yields of corn produced by 

 supposedly optimum cultivation as compiired with mere weed 

 elimination. 



The experiments were made b}' having two plots or sets 

 of plots, one of which received no cultivation after planting, 

 the weeds being kept down by a horizontal stroke of a sharp 

 hoe at the surface of the soil, particular care being taken not 

 to disturb the soil or to form a soil mulch; the other set of 

 plots received the usual cultivation. 



This work was carried on by the D'^partment of Agri- 

 culture for six years (190(1 to 1911) in C"-op»ration with 

 severrtl State agricultural experiment stntions and with 

 farmers, many of wh^m were graduates of agricultural 

 colleges. The results of 12.5 experiments are recorded in 

 this bulletin, including the early experiment-station tests. 

 The seven years' work in Utah is given separate discussion. 

 Of the 12.5 experiments 124 record grain yields and fifty- 

 five give fodder yields, 



A general average of all of these exieriments shows 

 that the weeded plots produced 95 1 per cent, as much fodder 

 and 99 lOfe per cent, as much grain as the cultivated ones. 

 If there was any difl'erence between either set of plots in 

 regard to thoroughness in keeping down weeds it was in 

 favour of the cultivated plots. 



Although it remains to be demonstrated how far this 

 principle may be applied in any particular section, as 

 a general average for all the regions in which this work was 

 done, it may be concluded that the proposition just stated n 

 substKiitially true. If thi.-! be accepted, weed control 

 becomes the principal oliject of cultivation. 



Weeds may be attacked in two ways: (1) by the use of 

 tillage implement", the primary purpose of which is their 

 eradication: and (2) by adopting cropping systems having 

 that object in view. 



