252 DISEASE IN PLANTS. 



Fasciated Dandelions, Crepis^ monstrous Chrysan- 

 themums, peloric Linaria, five-leaved Clovers, 

 spiral Teazels, etc., may all, if grown with care, be 

 kept more or less constant in the monstrous state. 

 That is to say, the particular kinds of variation 

 here manifested can be maintained in proportion 

 as the external conditions controlling the variation 

 are maintained. Such conditions are chiefly rich 

 supplies of food-stuffs, plenty of water and air, 

 suitable temperature and lighting, etc. Mutilations, f 

 favouring the development of abnormal buds may ; 

 also induce fasciations. 



Torsions or spiral twistings of stems also 

 frequently arise among plants grown in rich 

 soils, and are often combined with fasciations 

 e.g. Asparagus, Dipsacus; and De Vries has shown 

 that the peculiarity is not only transmissible b}' 

 seed, but may be more or less fixed by appro- 

 priate culture. 



Contortions of stems are often due to the 

 unequal growth on different sides of the stems 

 owing to the presence of fungi e.g. Caeovia on 

 Pines, Aecidiian on Nettles, also Puccinia on 

 petioles of Mallow, Cystopus on inflorescences of 

 Capsella, etc. 



Distortions of roots may be brought about in 

 various ways by the hindrances afforded by stones. 



Spiral roots occur occasionally in pot plants. 



Flattened roots usually result from compression 

 between rocks, the young root having penetrated 

 into a crevice, and been compelled to adapt itself 

 later. The distortions of stems by constricting 



