We made some trials with Abies communis and pectinata, by pinching with wire the leading and all the lateral shoots excepting one.  But we believe that they were too old when experimented on; and some were pinched too severely, and [page 188] some not enough.  Only one case succeeded, namely, with the spruce-fir.  The leading shoot was not killed, but its growth was checked; at its base there were three lateral shoots in a whorl, two of which were pinched, one being thus killed; the third was left untouched.  These lateral shoots, when operated on (July 14th) stood at an angle of 8o above the horizon; by Sept. 8th the unpinched one had risen 35o; by Oct. 4th it had risen 46o, and by Jan. 26th 48o, and it had now become a little curved inwards.  Part of this rise of 48o may be attributed to ordinary growth, for the pinched shoot rose 12o within the same period.  It thus follows that the unpinched shoot stood, on Jan. 26th, 56o above the horizon, or 34o from the vertical; and it was thus obviously almost ready to replace the slowly growing, pinched, leading shoot.  Nevertheless, we feel some doubt about this experiment, for we have since observed with spruce-firs growing rather unhealthily, that the lateral shoots near the summit sometimes become highly inclined, whilst the leading shoot remains apparently sound.

A widely different agency not rarely causes shoots which naturally would have brown out horizontally to grow up vertically.  The lateral branches of the Silver Fir (A. pectinata) are often affected by a fungus, Aecidium elatinum, which causes the branch to enlarge into an oval knob formed of hard wood, in one of which we counted 24 rings of growth.  According to De Bary*, when the mycelium penetrates a bud beginning to elongate, the shoot developed from it grows vertically upwards.  Such upright shoots after-

* See his valuable article in ‘Bot.  Zeitung,’ 1867, p. 257, on these monstrous growths, which are called in German “Hexenbesen,” or “witch-brooms.” [page 189]

wards produce lateral and horizontal branches; and they then present a curious appearance, as if a young fir-tree had grown out of a ball of clay surrounding the branch.  These upright shoots have manifestly changed their nature and become apogeotropic; for if they had not been affected by the Aecidium, 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 Aecidium, they “assume an erect habit.”  Dr. Stahl informs us that he knows of several analogous cases; and these seem to be closely related to that of the Abies.  The rhizomes of Sparganium 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.**