April 7, 192 1] 



NATURE 



171 



portant to observe to what a large extent sugar is 

 present as a reserve material in many of the ordinary 

 root crops such as the turnip, swede, etc., and in 

 the other varieties of the genus Brassica. It is not 

 generally recognised how much of the nutritive value 

 of cauliflowers, cabbages, brussels-sprouts, etc., is due 

 to the large amount of reserve sugar which these 

 plants contain, and this sugar is not present in the 

 edible parts only, but more particularly in the stalk 

 and petioles, which are extensively used as storage 

 organs. 



No quantitative analysis has been undertaken to 

 determine the amount of sugar present in these 

 organs, but a qualitative test with Fehling's solution 

 indicates that the amount of sugar must be consider- 

 able. This sugar is directly fermentable by yeast, no 

 hydrolysation being required. If the stem or petiole 

 is crushed under water and boiled to ensure the com- 

 plete liberation of the cell-sap, and yeast added at a 

 convenient temperature, alcohol can readily be de- 

 tected by the iodoform test. By the same process it 

 is easily demonstrated that fermentable sugar is also 

 present in the petioles of the swede and turnip. 



It is suggested that in the many thousands of tons 

 of cabbage stalks and petioles and of the petioles of 

 the turnips and swedes, at present a by-product of 

 farms and market-gardens, we have a suitable and 

 readily available material which could be collected 

 and utilised as a source of industrial alcohol. 



We learn from the returns of the Ministry of Agri- 

 culture for 19 1 9 that more than 72,000 acres were 

 devoted to the cultivation of cabbage, sprouts, cauli- 

 flower, and broccoli ; and upon a single farm in the 

 North of England as many as 40,000 cabbages were 

 grown in the year 1920. The returns of the Ministry 

 of Agriculture estimate that 14,200,000 tons of turnips 

 and swedes were grown in 1920. When these crops 

 are harvested an enormous residue must be annually 

 wasted which would be capable of producing a very 

 large quantity of fermentable sugar. The amount, of 

 course, would fall far short of commercial require- 

 ments, but it would be by no means negligible, and 

 might materially add to our resources for the pro- 

 duction of alcohol in this country, reducing the im- 

 portation of raw substances for that purpose, and 

 possibly to some extent also the importation of petrol. 



Moreover, many other plants could also be utilised. 

 Comparatively little attention seems, at present, to be 

 given to our native plants which store up large 

 quantities of starch or sugar as reserves. In the 

 Gramineae sugar is largely employed as a reserve 

 material, and it is not surprising to find that the 

 rhizomes of the couch-grass (Agropyron repens) and 

 the uni-internodal corms of the bulbous oat-grass 

 (Arrhenatherum avenaceutn) possess a large sugar- 

 content, the maximum amount being present in 

 autumn or early winter. This sugar varies with the 

 season of the year ; in autumn it is chiefly cane- 

 sugar, which on the approach of spring is converted 

 into glucose previous to being utilised by the plant. 

 In either case the reserve sugar in these plants is 

 fermentable by yeast without any further preparation. 

 Both these grasses are pernicious weeds, and large 

 quantities are annuallv eradicated from the land. 



Another source of raw material worth mentioning 

 for the production of alcohol is the starch 

 which occurs so abundantlv in the rhizome of the 

 bracken-fern (Pteris aquUina). Although it would 

 seem that this carbohydrate cannot be rendered avail- 

 able for human food, further research may indicate a 

 method for its profitable utilisation for power alcohol, 

 and it mav be pointed out that a natural process of 

 hydrolysation would take place in the spring as a 

 necessary part of the plant metabolism. At the 



NO. 2684, VOL. 107] 



present time there are many hundreds of acres covered 

 with bracken which might with advantage be re. 

 claimed for agricultural purposes, and the first stage 

 in this reclamation might well be the eradication of 

 the Pteris rhizome for utilisation in the production of 

 alcohol. 



Investigations at the present time tend largely to 

 concentrate upon synthetic processes, or to the explora- 

 tion of new plants which could be grown for the 

 production of alcohol, or to the extension for this 

 purpose of the acreage of food-crops such as potato, 

 beet, etc. The object of this letter is to direct atten- 

 tion to the enormous amount of suitable materials 

 ready to hand and at present overlooked and un- 

 utilised in our own country. The plants already 

 enumerated could be added to {e.g. the roots of the 

 spear thistle, Carduus lanceolatus, contain an abun- 

 dance of inulin), and no doubt systematic search 

 would reveal many more which could be exploited 

 for their unsuspected and valuable carbohydrate 

 reserves. The amount in the aggregate would 

 be very considerable, the cost of collection and 

 manufacture would be relatively small, and an asset 

 might thus be secured which would help towards the 

 solution of a pressing industrial problem. 



M. C. Potter. 



Armstrong College, Newcastle-upon-Tyne, 

 March 9. 



Relativity, Space, and Ultimate Reality. 



As one who has studied very carefully, so far as 

 his mathematics will take him, the various points of 

 view brought together in Nature of February 17 by 

 the great exponents of the doctrine of relativity, may 

 I have space to express the conviction that the press- 

 ing need at the present stage is a clarified conception 

 about the nature of pure space in relation to objec- 

 tivity or subjectivity? Let me define the contention. 



There is little difficulty now about the modest and 

 reasonable earlier demands of the relativists that 

 spatial directions are significant only in relation to 

 matter, that time cannot be dissociated from space, 

 that we have no criterion of absolute motion, and the 

 like. According to these representations space is con- 

 tingent upon the existence of matter and energy, so 

 that : extinguish the physical universe, and space as 

 an objective reality vanishes too. But the relativists 

 seem now to be taking the op{X)site point of view, 

 and in the attempt, so powerfully controverted by Sir 

 Oliver Lodge, to geometrise physics they indicate 

 that space, instead of being conditioned by matter, is 

 itself the foundation of matter and physical forces — 

 which are merely the " outcome of the geometry of 

 the universe," as Prof. Weyl puts it. Herein there 

 seems to lie a discrepancy in the relativist position 

 which needs clearing up. 



Now I take it that the following propositions will 

 be conceded : — (i) The geometries of Riemann in 

 any number of dimensions are in themselves purely 

 mathematical conceptions ; (2) the particular geometry 

 which fits our actual physical universe constitutes a 

 space-time system of four dimensions; and (3) our 

 sole experience concerning the objectivity of space 

 is derived from the property of matter which we call 

 extension, involving the notion of distances. But 

 where are we if we discard a universal connecting 

 medium, a sub-material "aether" connecting all 

 bodies in the universe as a necessary physical condi- 

 tion of every gravitational and electromagnetic field? 

 Banish the aether, and the only physical reality between 

 the members of the solar system is light occupying 

 otherwise "empty space"— a conception difficult to 

 entertain and to reconcile with the relativity -of pure 



