20 REACTION OF HOST TO PARASITIC ATTACK. 



uscans, which may, in addition, bring about death of the whole 

 shoot. Needles of spruce beset by aecidia of Chrymmy.ra 

 rlwdodcndri are cast after reproduction of the fungus in August 

 or September, while with Chrysomyju ahietis the needles of 

 Conifers fall in May. The latter examples diff'er somewhat 

 from the former in that the mycelium lives in the witches' 

 broom for years, and continues to send out new shoots with 

 deformed needles, whereas in the Chrysomym attack the my- 

 celium is confined to the needles and falls with them. 



Examples from other groups of fungi are the witches' brooms 

 of Alnus incana caused by Exoascus cinijhyllus. The leaves of 

 these are fully developed though somewhat modified in form ; 

 their life-period is, however, shorter than that of normal leaves, 

 and they fall earlier. It may be observed here that this 

 phenomenon of premature defoliation is one recorded as a 

 consequent of many parasites. The witches' broom twigs of 

 the alder grow and produce buds almost normally, yet the 

 whole broom-system dies in a few years, and long before the 

 normal life-period of the tree. 



The war of extermination by mycelium against host-plant 

 may frequently last for a very long time. Hartig gives an 

 example of a larch which had carried on the combat with the 

 larch-canker (Fcziza Willkommii) for over eighty years, l)ecause 

 during active vegetation of the host the parasite was unable to 

 make headway. 



D. Premature Development of Buds. 



The unfolding of buds in spring in advance of those of 

 normal plants is also a feature of many diseased plants. This 

 is manifest in the earlier unfolding of buds on witches' brooms 

 of the silver fir and cherry. The alder witches' broom, already 

 referred to, is however exceptional, in that its buds open after 

 those of normal twigs.^ 



A premature flowering may also result, so that flower-buds 

 formed in summer unfold the same autumn instead of during the 

 following spring. Thus in a recent autumn a violet opened 

 in a plot in the garden of Professor Hartig in Munich. The 

 flower was found to be somewhat stunted, and its stalk beset 



1 Smith, " Untersuchuiigen d. Aiiat. u. Morpli. der tlurch Exoasceen veru- 

 sachten deforniationen." Inaug. Diss. Muuicli, 1 894, p. 1(5. 



