30 



REACTION OF HOST TO PARASITIC ATTACK. 



Still more striking are certain structures resembling witches' 

 brooms, which are produced on Thujopsis dolahrata in Japan, under 

 the influence of the mycelium of Cacoma deformans (Fig, 8). 

 These consist of leafless non-chlorophyllous axes, dichotomously 

 branched, and with each branch ending in a disc. They arise 

 from shoots or leaves of the Thujopsis where structures of the 

 kind would never have arisen normally, and are wholly sub- 

 servient to tlie reproduction of the fungus, which forms its 

 sori under tlie epidermis of the terminal discs. 



Fig. S. Caeoma defrriuans. The nest-like structures are muoh-branclicd, 

 leafless shoots with each of their twigs ending in a caeoma-disc. (v. Tubeuf 

 phot.) 



The galls produced by Usfilaf/o Treubii on Polyfjonum Sacclm- 

 lincnsc are particularly interesting. Here, as a result of the 

 presence of the parasite, there are formed the so-called vegetative 

 canker-galls, and in addition, the fruit-galls, new organs derived 

 from lateral outgrowths of the host-plant, and of use only 

 in the spore-formation of the Ustilago ; they contain a special 

 capillitium-like tissue, and serve e.Kclusively for the shelter and 

 distribution of the fungus-spores. 



