188 THE EFFECT OF KILLING OB Chap. HI 



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 8° above the horizon ; 

 by Sept. 8th the unpinched one had risen 35° ; by 

 Oct. 4th it had risen 46°, and by Jan. 26th 48°, and 

 it had now become a little curved inwards. Part 

 of this rise of 48° may be attributed to ordinary 

 growth, for the pinched shoot rose 12° within the same 

 period. It thus follows that the unpinched shoot 

 stood, on Jan. 26th, 56° above the horizon, or 34° 

 from the vertical; and it was thus obviously almost 

 ready to replace the slowly growing, pinched, lead- 

 ing 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 grown out horizontally to 

 grow up vertically. The lateral branches of the Silver 

 Fir (A. pectinata) are often affected by a fungus, 

 Mcidium datinum, 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 be- 

 giiining to elongate, the shoot developed from it 

 grows vertically upwards. Such upright shoots after- 



• See his valuable article in are called in German " Hexen 

 Bot. Zeitung," 1867, p. 2.57, on besen," or " witch-brooms." 

 these monstrous growths, whicli 



