KKACTI'iX 



IfdST TO PARASITIC ATTACK. 



Tnii- atrophy is best seen in those cases where flower-forma- 

 tion is suppressed. This effect of parasitic fungi on their host is 

 by! n< i iiK-ans unconnnon, the fungus alone reproducing itself, 

 \\liil.- tin- assimilating host-plant remains sterile. This atrophy 

 is f. mini not only in annual plants, but also in those where the 

 symbiosis might be designated as perennial. The last-mentioned 

 case is exemplified in Aecidium chdinum, the witches' broom of 

 which never bears flowers ; again, by witches' brooms of Exoascus 



FIG. ^.Euphorbia Ciiwlxsias. A healthy flowering normal plant compared 

 with the attenuated non-flowering form inhabited by Aecidium euphorbias. 

 (v. Tubeuf phot.) 



wrasi (Fig. 5), which bears only leaves when the rest of the 

 tree, is in blossom. Another perennial symbiosis behaving thus 

 is shown in Euphorbia Cyparissias attacked by Aecidium 

 x'/'/tnrhiai'; year after year the diseased shoots produce only 

 leaves, which assist in the reproduction of the fungus (Fig. 6). 

 Similarly with many other Uredineae. 



Arrest of the seed occurs in ovaries of species of Primus under 

 the influence of Mvoasci (Fig. 7). In flowers attacked by Oystopus 



