SYMPTOMS OF DISEASE. 183 



The whole matter is compHcated by the 

 behaviour of certain variegated plants e.g. Ribbon 

 grass, Calla, Abutilofi, which are usually regarded 

 as partial albinos. 



Meyen showed long ago that such variegated 

 plants, if grafted on green ones, may induce the 

 development of variegated leaves on both scion 

 and stock, and Morren and others have not only 

 confirmed this but have also shown that variegation 

 may be inherited through the seed. Nevertheless 

 some care has to be taken with many of these 

 variegations lest rich soil, bright light, and other 

 favourable treatment favour the restitution of the 

 green colour. These facts may be interpreted in 

 various ways. Some disturbance of physiological 

 functions of the roots, due to unfavourable con- 

 ditions of soil, may be the cause ; but Beijerinck 

 has lately published some results which show 

 that some of these albino diseases can be induced 

 by inoculating normal plants with the juice of 

 spotted ones even though such juice has been 

 filtered through porcelain, and concludes that a 

 " contagimti fluidnni vivwn " of the nature of a 

 transmissible enyzme is the agent which disturbs 

 the physiology of the infected cells. 



Koning, while confirming these results in the 

 main, refers them to a micro-organism so small 

 that it traverses the porcelain filter. 



Upheaval of seedlings. This is a common form 

 of injury, resulting in death by drought and ex- 

 posure, especially in seedling pines, wheat, etc., in 

 soils exposed to alternate freezing and thawing 



