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Show 188 THE EFFECT OF KILLING OR CHAP. III. some no t en Ough · Only one case succeeded, nam. ely, with the spruce-fir. The leading s.hoot was not k1lled, but its growth was checked; at 1ts base th~re were t h ree l a t er.a 1 shoots in a w. horl, two of .w hwh were pinched, one being thus k1lled; the thud. was left unt ouc h ed · These lateral shoots,o when operha te·d on (Jul 14th) stood at an angle of 8 above .the 01~1zon; by §ept. 8th the unpinched one had nsen 35 0 ; by Oct. 4th it had risen 46°, ancl by Jan .. 26th 48, and it had now become a little cur:ed mwards .. Part f th. r·1·se of 48° may be attnbuted to ordmary 0 lS 2o . h' th grow th, f or. the pinched shoot rose 1 w1 t· mh d c s1am e pen·o d . It thus follows that the unpm. c e s 1oot 34 o stood, on Jan. 26th, 56o above the ho~lzonl' o~ t from the vertical; and it was thus ouv~ous y amos ready to replace the slowly growing, pmched, lead· . h t Nevertheless we feel some doubt about 1ng s oo . ' b d 'th th1. s expen.m ent, for we have since o serve 1 Wl 1 spruce-firs growing rather unheal~hily, that the ~tera shoots near the summit sometimes b~come highly inclined, whilst the leading shoot remams apparently sound. h t A widely different agency not rarely ca~ses s oo s which naturally would have grown out honzontal~y to grow up ver tl.C a llY · The lateral branches of thef Silver Fir (A. pectinata) are often affected by a ung~Is, lEcidium elatinum, which causes the uranch ~o enl:r~~ into an oval knob formed of hard wood, m ~n which we counted 24 rings of growth. Accordi~gbt~ De Bary * when the mycelium penetrates a bu ~t ginning ' to elongate, the shoot de ve 1o pe d fromft 1 grows verti.c ally upwar d s. S uc h upn:g ht shoots a er· * See his valuable article in 'Bot. Zeitung,' 1867, p. 257, on these monstrous growths, which are called in German '' I;~exen· besen," or " witch-brooms. CHAP. III. INJURING 'fHE PRIMARY RADICLE. 189 wards produce lateral ~nd horizontal bra~~hes; and they then present a cuno~s appear~nce, as 1f a yo~ng fir-tree had grown out of a ball of clay surround.mg the branch. These upright shoots have manifestly changed their nature and become apogeotropic; for if they had not been affected by the lEcidium, they would have grown out horizontally like all the other twigs on the same branches. This change can hardly be due to an increased flow of sap into the part; but the presence of the mycelium will have greatly disturbed its natural constitution. According to Mr. Meehan,* the stems of three species of Euphorbia and of Portulaca oleracea are "normally prostrate or procumbent;" but when they are attacked by an JEciU.ium, they "assume an eree~ habit." Dr. Stahl informs us that he knows of several analogous cases ; and these seem to be closely related. to that of the Abies. 11he rhizomes of Spargani1t·m ramosum grow out horizontally in the soil to a considerable length, or are diageotropic ; but F. Elfving found that when they were cultivated in water their tips turned upwards, and they became apogeotropic. The same result followed when the stem of the plant was bent until it cracked or was merely much bowed.t No explanation has hitherto been attempted. of such cases as the foregoing,-namely, of secondary radicles growing vertically downwards, and of lateral shoots growing vertically upwards, after the amputation of * 'Proc. A cad, Nat. Sc. Philadelphia,' June 16th, 1874 and July 23rd, 1875. ' t See F. Elfving's interestin()' paper in' Arbeiten Bot. Institut 111 Wiirzburg,' vol. ii. 1880, p. 489: Carl Kraus (Triesdorf) had pre-viously observed (' l!..,lora,' 1878, p. 324) that the underground shoots of 'l'riticum repens bend verticA.lly up when the parts above ground are removed, and when the l'hizomes are kept partly immersed in water. = 1:~; • :r~. ,t. ::~1 •• ! •• ~ l :~: :: ' :;; ~; f :~· :: ~ ,,,I ~ :P I' j"J'l I'f 1·.•- l:;·li,)1l1l |