6?o 



NA TURE 



[OcTor.iiK 24, 1895 



in winter .iiui siMiiiiiLr .-carch the mountain tops for their slock, 

 are the men liest fitted to tell us about the habits of the bird. 

 On obsen'ations made during such experiences Mr. White Uises 

 his own account. In the district with which this writer was 

 acquainte<l. the kea always live^ high up on the mountains, 

 among rocks and boulders, a long distance above the forest-line ; 

 in such a situation, of course, berries and fruits were out of the 

 question, and the bird apjHsired to live on lichen and any insects 

 it could find. Even when the ground w.-is covered with several 

 feet of snow, and when roots and other food were out vi reach, 

 lichen growing on sleep rocks would still be obtainable liy the 

 bird. The view that the diet of the kea generally consists of 

 fruit and lierries would thus appear to be erroneous. 



It will be reniemlieretl that Wallace and others state that the 

 kea regards the kidneys of sheep as a " special delicacy," and 

 that it attempts lo birrow mto its victim in such a way as to 

 reach this |iarl. Mr. White, however, op|X)ses this jirevalent 

 view, and regards it as proKible that the bird desires to obtain 

 the blooil of the sheep rather than the kidneys ; and in support 

 of this view states that he has never seen a dead sheep attacked 

 by keas. The fact that the kea so frequently pierces the body 

 of a sheep in the region of the kidneys is due to the position it 

 takes on the back of its victim to maintain a firm hold — a |x)sition 

 from which it cannot be easily dislodged, as it could fri>ni the 

 head or rump of the sheep. In corroboration of this Mr. White 

 mentions that sheep with long wool are more frequently attacked 

 than animals w ith .short wool ; as apiKirently the long wool gives 

 the bird letter facilities for holding on with his feet when 

 drilling a hole into the Ijack of the .sheep. It is not very easy to 

 conjecture how this habit of attacking sheep was first acquired 

 by the kea. In winter time the sheep are covered with snow, 

 and often have icicles hanging to their wool ; and it is suggested 

 by Mr. White that keas may have mistaken sheep so tlisguised 

 for snow -covered |xitches of rock. It may further have hai)i>ened 

 that when .searching the supposed rocks for insects the birds in 

 some cases would laslc the blood of the sheep. " When some 

 of the birds had once found out that the blood of the sheep was 

 good for foofl, others were .soon initiated into the performance.' 

 It" is po.ssible that in some such manner the kea may have 

 gradually acquired this curious and unattractive habit which 

 renders the bird such a |icsl to the New Zealand farmer. 



W. CiAKsi am;. 



THE PENETRATION OF ROOTS INTO 

 LIVING TISSUES. 



'T'lIK ca|)acity ix>.s.scsscd by the roots of certain ixirasiles, 

 ^ such as Ciisriila, lo ]x;netralc into (he tissues of their host, 

 is apparently an unique, not to say a remarkable phenomemm. A 

 little reflection, however, upon the powers of roots In general, 

 leads us to doubt whether this properly is really as restricted 

 as the first glance would lead us to imagine : and when we 

 |>crusc Prof Tfeffcr's work u|X)n Ihe pressure of the root, and 

 finrl that, for instance, the root of the common bean exerts 

 fluring it-s growth a pre.ssure of .some 400 gms. , we realise that 

 this mechanical action alone might suflicc to drive the growing 

 root of most plants into living ti.s.sue, if circumstances neces- 

 sitated such an ex|K:(liency. This is evidently an im|)orlanl 

 joint, and touches u|Km Ihe evolution of the higher parasites: 

 It is only remarkable ihat it has .so long remained luilouched. 

 We must now thank (leorge I'eircc for taking up this neglected 

 ,,il,i, ri. ,Tnd placing it U|ion a sure basis (see /Vu/. Ziir. .September 

 The question first to be decided was whether the.pres- 

 ■ hich I'fefTer had found in the growing roots was in itself 

 ht lo force Ihe rorjts ihrrmgh living tissue. I'or the 

 iiination of this, iron mo<lels of roots weighted up to 

 in.s. were employed. The apices of these were pl.iced 

 ■ cul>e cut from a |>otatf), and the whole surrounded with 

 "lust lo keep Ihe living substance fresh, .\fter an 

 venly-lhrec hours, il w.is found that the iron point 

 r .led ij m.ni. into the potato. .Again, a similar model 

 "' i.'iiUil lo 320 gms. was driven in twenty-four hours through 

 iK. ..rk layr and 2 in.m. of |>arenchyma of an uncut jxitato. 

 I placed on the stem of Impatiem sii/laiii, one 

 letrcK Ihick, pierced this in less than twenty 

 ins. weight were employed. 

 ir inferior lo that found by rfeflfer in the root 

 I- »uf)icienl lo drive an ir<m miKlel an appre- 

 cuiblc dulancc through ihe living li&sucs of the potato. 



It was far trom certain, howexer. wiielher a jiressure whicli 

 was ample to imi>el a rigid iron rodlet against a considerable 

 resistance would have equal efiiciency in the case of a root, the 

 pressure in which arose from so uncertain and inextricable a 

 source as its life. 



There were many facts both fro and ninlra. 



The acid substance or substances, which it would seem that 

 most roots excrete during their growth, might possibly facilitate 

 the root's power of penetration. Just as niany fungi eat thcii 

 way, as it were, into the solid wood of their host by means of 

 ferment-like substances which they secrete and |X)ur out upon 

 their substratum, so might the roots perhaps be expected to 

 soften and prejiare their way by means of their acid excretions. 

 .\gainst the supiwsiiion could be raised the fact, already broached, 

 that the forces. imiK'lling the root-apex forwaril, are derived 

 from the vital .ictivities of that structure, and than lhe.se nothing 

 can be more .sensible to change of surroundings, or less to l)e 

 reckoned upon by us, whose conceptions of anything dealing 

 with life are yet shrouded over with the darkest obscurity. 



But to jxiss from speculation to facts, we find that Peirce 

 tested this ]K)int by experiments on the seedlings of Brassica 

 iiapui ami Siiia/iis alha. He look a i^otato, and s]ilit it in half: 

 on one of the halves he cut a number of small slits, into each of 

 which he inserled a seed of the plant under observation. He 

 then placed the potato-h.ilves together, binding them 

 tightly with .string. The whole contrivance w;is jilaced in a 

 vessel containing damp sawdust, care Iwing taken that the cut 

 surfaces of the tuber lay horizontally. After an interval of 

 twelve days the specimens were examined, and although some 

 were found to have grown lietween the cut surfaces (for nearly 

 all had germinated), yet others had pushed their roollels verti- 

 cally downwards so as lo penetrate the substance of the potato. 

 In some instances so vigorous had been the growth that the 

 rootlet had traversed the whole thickness of iwrenchyma. 

 pierced the har<l corky layer of the surface, and then reached 

 the sawdust without. 



Anatomical examination of the root anil surrounding polalo 

 tissue showed several peculiarities. In the first place, the young 

 root w.as almost devoid of the customary clothing of h.iirs : 

 secondly, the cells of the potato had undergone alteration, inas- 

 much .as those which were in immediate contact with the 

 advancing root were much contorted and torn, whilst two or 

 three layers neighbouring on the injured elements h.ad undergone 

 division by walls parallel to the long axis of the root, and had 

 subsequently become corky in nature. By this means the 

 intrusive rootlet was enclosed within a corky cylimler or sheath, 

 cutting it off more or less iK'rfectly from Ihe living, unharmed 

 tissue of the tuber. The starch grains were in every case 

 unaltered, but Primet, ni his research on Cyiiodoii, and Peirce, 

 in his examination of one of his specimens of Pisiiiii, noticed 

 certain grains in the neighbourhood of the root apex which were 

 partially disintegrated. This, however, is not a neces.sary con- 

 seciuence of ferment action ; indeed, a check experiment of 

 I'eirce's leaves little doubt thai the disintegration results in these 

 cases from the activities of bacteria w liicli had gained an entrance 

 with the root. ( dass tubes dosed and pointed at one end were 

 sunk, like the iron models already mentioned, into pot.alo tissue. 

 In one instance the apes of the glass was surrounded by 

 "corroded" .starch-grains. Here there could be no question 

 of ferment formation, and evidently l>.acteria were adherent lo 

 ihe a))ex. 



"So far the experiments had proved lhat the thin, delicate, 

 .inil pointed roots of raiw and while mustard are able to 

 penetrate living tissues. Peirce carried the matter further by 

 testing the powers <ti the blunt roollels of /V.tHwand X'icin faha 

 to do likewise. The roollels of germinal ing .seeds of ihese were 

 placed in gla.ss lulies into which they accurately fitted, and 

 their apices pj.aced in contact with the surface of a cube of 

 potato. The seed and gjass tube were rigiilly held by layers 

 of gypsum, in which a gap was left for the exlensi()n of the 

 plumule. The whok- was kept ni'iist by damp sawdusl. After 

 three days the pkiIs were found to have pierced Ihe living tissue 

 lo the extent of 75 111. m. 



')ther cxix;rimenis were made im the Siime plants in which 

 other tissues, such as slem of liiipatiriis siillaiii, leaves of 

 Kchevaria ami .Aloe, petioles of Kheum, \c., were .substiUiled 

 for Ihe |)olato. These also were penetrale<l by the rootlets. 



In w>me inslances, however, such as leaves of Aloe and 

 |>elioles of R/iciiri off'uiiialc, the pabulum was evidently un- 

 siiited to the healthy existence of the root, for :ifter a short 



NO. 1356, VOL. 52] 



