666 



NATURE 



[January 20, 192 1 



statement that this English vowel is a diphthong 

 composed of two vowels is incorrect. The vowel is 

 a single sound that gradually changes greatly in 

 character. There is no objection to calling it a 

 diphthong provided it be recognised — as the 

 speech curves show — that all diphthongs are really 

 sing-le vowels that change greatly in character. 

 At the same time, it must be recognised that what 

 is called a single vowel may change even more 

 in character than a so-called diphthong; the 

 change in a very short vowel, as in "but," is 

 often surprising. 



Just what constitutes the differences between 

 the different vowels is a problem at present beyond 

 the reach of science. The ear tells us that there 

 are many sounds which we group together under 

 the type "ah"; many others that would go to 

 form the type "00," etc. The speech curves show 



that the multiplicity of varieties under each type 

 is almost beyond belief. In a general way we 

 know that the impression from " ah " is that of 

 a higher tone than from "00," from "ee" higher 

 than from "ah," and so on. All details of the 

 tones in a single vowel are lacking. Every in- 

 vestigator has differed from every other one in 

 regard to what tones constitute any particular 

 vowel. As shown in this article, we can get so 

 far as to say on what principles a vowel is built 

 up. We can even get curves of the vowels of 

 an accuracy that leaves nothing to be desired. 

 We have not, however, any method of analysing 

 these curves accurately into a series of frictional 

 sinusoids with independent periods and factors of 

 friction. We must probably wait for some mathe- 

 matician to do for this problem what Fourier did 

 for harmonic motion. 



Toxic Root-interference in Plants. 



THE earlier investigations of the late Mr. ] 

 Spencer Pickering at the Woburn Experi- ■ 

 mental Fruit Farm on the action of grass on fruit ; 

 trees, which were described in the third (1903) and 

 thirteenth (191 1) repyorts issued from that station, 

 sufficed to show that, in spite of some variability 

 in degree, there is a definite deleterious effect on 

 the health and development of fruit trees caused ! 

 by grass grown immediately around them. That ' 

 this is a general result and not a matter of special 

 soil or other local conditions at Woburn has been 

 demonstrated by independent experiments con- 

 ducted in this country at Long Ashton, Wisley, 

 and other places. So marked is the crippling 

 effect of the grass in some cases that death of 

 the trees has resulted. On the other hand, the 

 presence of numerous grass orchards in appar- 

 ently healthy and vigorous condition in many 

 parts of the country made the existence of any \ 

 direct toxic action on the part of the grass, such 

 as Mr. Pickering was led to postulate, appear 

 doubtful. It was evident that the action, if any, j 

 must be relatively complex, and the later work 1 

 at Woburn now shows that this is so. In the 

 seventeenth (1920) annual report from that centre 

 new evidence is recorded which indicates not only '. 

 direct toxicity of grass on fruit trees, but I 

 also a similar effect for any one plant on 

 another when the two are grown in close 

 association. 



It is therein claimed that the action of grass , 

 is shown to be due to toxic substances derived ' 

 from the grass, and is not the indirect result of any 

 adverse effect on soil conditions as regards aera- 

 tion, available moisture, or pJant food. In a 

 .series of experiments in which apple trees were , 

 grown in pots and the grass in shallow, perforated 

 trays resting on the soil of the pots, the injurious 

 effect was secured, notwithstanding- that the grass 

 roots, by being confined to the soil in the tray, 



NO. 2673, VOL. 106] 



could neither impoverish the soil in the pot below, 

 nor deprive it of oxygen or water. A similar 

 result was obtained when the grass was grown 

 in sand, instead of soil, in the perforated trays. 

 The presence of grass roots in the soil in which 

 the tree was growing was thus immaterial for the 

 manifestation of the dwarfing effect, and it follows 

 that nothing which might be abstracted from the 

 soil by them could be held accountable for the 

 results. The conver.se view that grass added to 

 the soil something deleterious to the tree appears 

 to offer the only explanation, the toxic material 

 presumably being conveyed from the trays to the 

 soil in the pots by means of the drainage w-ater 

 from the former. Direct evidence was secured on 

 this point by utilising for w-atering the trees the 

 leachings from the grass trays, the trays in this 

 case not resting on the soil of the pots, but being 

 placed elsewhere. The injurious effect on the tree 

 was as marked as before. When, however, the 

 leachings were allowed to stand for twenty-four 

 hours exposed to the air before being used for 

 watering the pots, the trees apparently were un- 

 affected. 



It was considered by Mr. Pickering that these 

 experiments prove that the leachings contain an 

 oxidisable substance derived from the roots of the 

 grass which in its unoxidised form is detrimental 

 to the growth of the trees, but after oxidation 

 is no longer of a toxic character. The suggestion 

 that it is nothing more than carbon dioxide given 

 off by the grass roots was, according to him, dis- 

 proved by the results of a series of experiments 

 in which the plants were grown in pots as above, 

 " with or without a surface crop in the trays, 

 watering them in one case with ordinary water, 

 in another case with a saturated solution of carbon 

 dioxide, and in a third case with clear lime water, 

 which, since lime absorbs carbon dioxide, would 

 presumably have the reverse effect of the carbon 



