EFFECT OF I'AKASITK IVM.I (>N THE Fi'lI.M OF HsT-l'LANT. 29 



at the same time tleshy and of a bright rose-red colour ; tin- 

 ovules are sterile or abnormally formed. "Wakker, however, 

 found no very marked change in the anatomical structure of 

 .such tlowers. 



The species of the Exoasceae also produce striking hypertrophy 

 of flowers. Thus there are the sac-like outgrowths of the 

 catkin-scales or ovaries of poplar caused by Tnjiln-inn Johan&onii 

 and T. //* rj'j>//<>,'c < Fig. 52), and tin- "pocket-plums" or "fools" 

 due to Exoascu* pruni (Figs. 49 and 51). In these last- 

 nu-iitioned cases, the outer layers of the ovary become thick and 

 Ik-shy, sometimes remaining green, while the stone and kernel 

 remain rudimentary. The aider, under the influence of .Vn/ /*///. > 

 a J ni incanae, has the catkin-scales much enlarged, deprived of 

 chlorophyll, and of a red colour (Fig. 53). 



Mummification, or the transformation of the fruit into a fungal 

 resting-body or sclerotium, is not unfre<puent. In some respects 

 this process resembles the change in ovaries brought about by 

 Ustilagineae. Here, however, we have to do neither with hyper- 

 trophy of the fruit, nor yet with its complete destruction. The 

 best-known sclerotium is that of Cl<tri<;j,.-< purpurea i Fig. 84). 

 It first fills up the base of the ovary, then kills it and -rows 

 out as ;i large horn-like sclerotium. The sclerotium of tin- oak 

 (Sderotinia Hot^-hunm) completely replaces the acorn, leaving 

 only the outer covering enclosing it. Likewise, in the mummified 

 berries of bilberry, cowberry, erowberry, cranberry, and others, 

 one finds the normal parts almost wholly replaced by the 

 resting-mycelium of some species of &/, ,;,/;;</. 



Formation of new Organs. 



Although parasitic fungi commonly induce hypertrophy of 

 tent organs and development of normal latent structures, 

 they a iv seldom associated with formation of new organs. A- 

 -uch. however, we iiiu-t iv^a rd the formation of adventitious 

 buds on the fronds of /'/, ,-/'\ <///n</, /'///> ,,'/, 1,'et/, and A^jiiil in m 

 iiri*lftnii, Sw., under the inliuence of 7'nji/i n'/i" Lain;, 

 and 7'. Cxi-iin cervi, respectively. 1 I'.uds ..r bulbil- of this 

 kind occur normally on several specie-, ..f fem>: but in tho<e 

 ju-t mentioned lhe\ appeal' only as a iv-nll of the para-iie. and 

 develop into structure- reinindiii-j one of a witches' broom. 



' < iir.-t-lili.-iL'i-li, /'/.. /vi. 



