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TEE GABDENEBS' CHBONICLE. 



[July 28, 1888. 



is a rough one. Many old analyses indicate 

 they do not. Trade catalogues, which give the 

 percentage of starch in different varieties, show 

 what a difference there is in the amount of starch 

 present. (Whether these percentages are given on 

 the authority of actual analyses, or have been 

 obtained by some such apparatus as the amylometer,* 

 shown at South Kensington in 1876, or the fecu- 

 lometer, I have not been able to learn.) Of what 

 is the remainder of a tuber composed? It is a 

 question of interest to every consumer to know this, 

 and whether the remainder is as digestible as starch. 

 If all tubers consist entirely of starch granules, why 

 should some behave so differently from others as they 

 do, when boiled— some being " waxy," some " mealy 

 as a ball of flour," and some " watery " ? 



When I told a Covent Garden dealer the kind of 

 interest I take in Potato growth, he laughingly 

 replied he thought I should find cultivators said like 

 Topsy, '"xpect they growed," and never bothered 

 their heads about the chemistry of a tuber. I can 

 hardly believe that this is so now, however true it 

 may have been twenty years ago. If so, there is 

 less attention paid to Potato culture than to cereals. 

 But he is more likely to know than I, who can only 

 guess how far cultivators study their crops. 



Professor Phillips in his memoirs of William Smith 

 has preserved an anecdote of an agricultural meeting 

 at Longleat about the year 1800. Mr. Davis, steward 

 to the Marquis of Bath, observed to a farmer that 

 he had not seen him at the last meeting. " Why 

 noa, zur : I been thinking, zur, these agricultural 

 meetings don't do much good." " I tell you what, 

 my friend : they have done some good if they have set 

 you thinking, for that is what you never did in your 

 life before ! " If I set some cultivators, who can 

 work out the questions, thinking how a tuber is 

 formed, though they may never have thought about 

 the subject before, I shall accomplish just what I am 

 aiming at. 



We all know the old saying, that a fool can ask a 

 question that it puzzles a wise man to answer. 

 But questions have a use if they set anyone at work 

 to answer them. Indeed, in every intentional ex- 

 periment (as distinct from an accidental experience), 

 we must first have the question quite clear which 

 the experiment is designed to answer. 



Progressive Accumulation of the Starch. 



About this time last year it occurred to me that 

 an interesting preliminary step would be to examine 

 Potatos from the same plot of ground at different 

 stages of their growth with regard to (1), The per- 

 centage of starch they contain, as ascertained by 

 actual analysis ; and (2), whether the starch was 

 equally distributed through the tubers. 



Messrs. Carter & Co., of Holborn, generously con- 

 sented to send plants at successive periods of growth, 

 and Mr. Robert N. Lennox, of the Royal Institution, 

 kindly undertook the consecutive analyses in his own 

 laboratory. The results will be more fully referred 

 to presently, but I wish to mention here that they 

 show these facts : — In the youngest specimens the 

 percentage of ash was 10 8, and of starch, 16'4 ; and 

 in the last sent the percentage of ash was '70, and 

 of starch, 24'4. The increase of starch was steady 

 all through the series, and the water steadily dimi- 

 nished from 805 per cent, in the earliest, to 70'6 in 

 the latest specimens. Further than this, the starch 

 was not equally distributed through the tubers, the 

 outer portions containing much more than the 

 inner. -Photographs of thin sections treated with 

 iodine show that the area of the greatest amount 

 of starch has an irregular boundary line, as 

 may be seen from the woodcut (fig. 8). Although 

 the ' woodcut hardly reproduces the delicate gra- 

 dations shown in the photograph it perhaps suf- 

 fices to illustrate the unequal distribution of the 

 starch granules. Iodine forms with starch, a com- 



* Exhibition oE Scientific Apparutua at South Kensington, 

 Catalogue No. 2737. Demby's Amylometer. F. H. Buchler, 

 Breslau. Said to have been quite new in 1875. Its merit is 

 stated to bo the simplicity and accuracy with which Potato 

 Btarch can be tested. 



pound, which has a characteristic blue colour. It is 

 the lighter portion of each section that indicates the 

 area of deepest blue — that is, the area of most starch. 

 Direct chemical analyses (as will be seen from the 

 tables below) on the outer and inner portions of 

 tubers confirm the fact, that there is more starch in 

 the former than the latter, though they, of course, 

 cannot, as the photograph does, show the gradations 

 of distribution. 



It would be absurd to attempt to generalise from 

 a series of analyses made on one variety only ; but 

 these resulcs are suggestive. A large number of 

 varieties growing in different soils, early and late 

 varieties that are subject to different climatic con- 

 ditions, would have to be examined and account 

 taken of temperature, rainfall, and sunlight, before 

 we could safely generalise on the rate of formation 

 of starch granules. The more delicate work of starch 

 formation in leaves, involving the use of appliances 

 for microscopical photo-chemistry could perhaps be 

 undertaken only by younger cultivators who have 

 had a training in scientific manipulation. But there 

 are many investigations I think cultivators might 

 undertake with a little trouble combined with syste- 

 matic method. With regard to published analyses, 

 there is one point that has often struck me. The 

 percentage of ash is almost always returned simply 

 as " ash," without any statement as to its compo- 

 sition. Queries : Is it the same in all cases ? Does 

 it depend on the soil ? or is the selective power of 

 the plant sufficient to overcome differences of soil ? 

 Do the compounds which the process of analysis 

 returns as " ash," pass in the growth of the tuber 

 through chemical changes that may affect the rate 

 of the formation of starch in the tuber ? We may 

 surmise on these points, but definite investigation ' 

 is what is needed. 



It must be borne in mind that the formation of 

 starch in leaves, which has been studied by Mohl, 

 Sachs, Pringsheim, Godlewski, Nageli, Schimper, and 

 others, is a different question from its formation in 

 tubers. Leaves form starch from which gases con- 

 stitute the air. In them the existence of starch 

 molecules appears to be but a passing stage to the 

 formation of other carbon compounds. Tubers form 

 their starch from the carbon-compounds already in 

 the plant. In them the starch (or most of it) 

 assumes the form of granules, and here it remains 

 more or less permanent till sprouting commences. 



Now, although I have been told that to talk 

 " chemistry " (as it is called) in asking questions will 

 only frighten most cultivators, I do not see how to 

 help it. It is frequently remarked by those who 

 regard only the changing nomenclature and changing 

 symbols used by chemists from time to time, that it 

 is no use trying to " learn chemistry," as every few 

 years it are " all altered ; " and such facts are re- 

 ferred to as that " carbonic acid," and " sulphuric 

 acid," and other familiar names, are not even to be 

 found in the index of the latest works. With the 

 cultivators, who, I am told, are frightened at 

 chemical names, I fully sympathise. It is at first 

 confusing to grasp the meaning of such a name as 

 " Triethylphenylammonium hydroxide." Some people 

 can gain knowledge more by sight than sound, while 

 others depend chiefly on remembering sound. It is 

 to many easier to see the meaning of the formula, 

 NC H 5 (C 2 H 3 ) S | better stil] in a formula in 



ri J 

 " rings," as is now more commonly done. 



Atoms and their Arrangement. 

 It is, of course, one thing for a chemist to ascer- 

 tain facts by experiments, and group his facts in 

 accordance with a theory applicable to all chemical 

 changes, and quite another thing to adapt some 

 representation of them for other people's informa- 

 tion, in words or by symbols. For myself I always 

 found it easier to follow the descriptive or 

 " Styptic formulze," the different coloured balls 

 of which represent atoms, and the little rods 

 joining them represent the force, or forces, 

 holding them together : the force we as yet 

 know nothing about. Whether we use the term 



" chemical affinity," " mutual attraction," " action 

 at a distance," or any other term we like, 

 we do not know what it really is we repre- 

 sent by our little connecting rods. We may soon 

 perhaps be able to represent it in such terms 

 as electricians use ; but as we do not yet 

 know what electricity is, we shall not even then 

 have advanced much in explanation. Every one 

 knows that, with a magnet under a sheet of paper, 

 we can move a steel needle above it, and we say we 

 move the needle because we move the source of 

 magnetism. But when there comes the question, 

 What is magnetism — what is this " action at a dis- 

 tance " ? we have no answer. We know that with a 

 magnet and an electric coil, battery, and wires we 

 can send messages. We can practically use elec- 

 tricity, though we do not know what it is. So with 

 chemical affinity. Our Arts depend on it, and we 

 use it almost at will, though we do not know what it 

 is. Our little rods to hold the balls together do very 

 well to represent it — to help us in our ignorance to 

 form a picture to our minds. We can manipulate 

 the balls to represent such chemical changes as we 

 think our experiments tell us. 



Equally we know very little about the atoms the 

 balls represent. For convenience they are made 

 spherical (for class purposes about the size of billiard 

 balls). But we do not know the shape of atoms or 

 even whether they have any definite or constant shape 

 at all. As regards their size — Sir William Thomson, 

 from the result of many calculations in four different 

 lines of research, has given, as a rough popular 

 illustration of the average size — that if a ball of 

 water, the size of an ordinary foot-ball, were 

 magnified to the size of the earth, the average 

 size of each component atom would then appear 

 about that of a cricket ball — perhaps three or 

 four times larger, perhaps as small as shot. We 

 may for present practical purposes leave out of 

 consideration the questions of the size and possible 

 shape of atoms, and what the " chemical affinity " is 

 that binds atoms together. It is worth noting that 

 Dalton, in his early work (beginning about 1802), in 

 studying atoms called them " particles," and did not 

 adopt the word atom for some years. In print he 

 made use of small circles with symbols to represent 

 different " kinds of atoms," carbon, hydrogen, 

 oxygen, &c. The plan that will here be followed is 

 that of enclosing the first letter of the name given 

 within a circle. 



Composition of Starch. 

 Thus the composition of a molecule (the sense in 

 which the word is used will be presently explained) 

 of starch is expressed as containing : — 



®©@©©© 



® ® i® ® ©, ® ® ® ® © 



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— that is, six atoms of carbon, ten of hydrogen, and 



five of oxygen,* often expressed thus : — C„, H 10 , 5 . 



To represent a molecule of fruit-sugar an additional 



® © 

 © 

 would| be needed. The grouping of the atoms in a 

 molecule will have to be considered. 



Though this method is hardly so striking as the 

 balls and rods, yet is is found by many that it can be 

 more readily understood than the formula C„ H 10 5 

 for starch, and C H^ O for -fruit-sugar ; while in 

 the change from carbonic acid and water to starch, 

 with oxygen set free, the change from starch to 

 sugar, or sugar to starch, it helps the mind to 

 picture the changes going on without troubling it 

 with figures. 



For illustrating what are the chemical changes in 

 plant-growth where balls and rods cannot be used 

 (as in manuscript or print) circles with connecting 



* That the numbers 6, 10 and 5 show the relative proportions 

 of O, H and O seems firmly established by all experiments. 

 Whether the numbers should be 12, 20 and 10, or some much 

 higher multiple, is not so sure.. 



