K.—BOTANY 187 
is caused by a bacterium, and Dr. Dowson is carrying out further investi- 
gations on this disease, an account of which will be given during the present 
meeting. 
Time does not permit me to deal with the important advances which 
have been made recently in our knowledge of the innumerable diseases of 
plants caused by viruses—some of which are of great importance—and of 
the properties of the viruses themselves, but Dr. Kenneth Smith, one 
of the most successful workers in this field, will discuss some of the more 
notable of these advances during the meeting. I will only add that these 
remarkable ultra-microscopic agents of disease should be of interest to all 
biologists for they may belong to a borderline territory between the living 
and the non-living. 
During the early development of plant pathology little attention was 
paid to the study of disease in plants of a functional kind, t.e. to disease 
not induced by parasitic agency. For a long time information about this 
class of diseases was fragmentary and vague, and in some respects this 
statement is still true. In certain ways non-parasitic diseases of plants 
are more difficult to investigate than those due to parasites, and not much 
progress can be made with the elucidation of some of them until more is 
known about normal plant physiology. Some notable advances have been 
made, however, in the understanding of certain diseases of this class, and 
some of these investigations have resulted in important contributions to 
plant physiology. This is especially true of diseases which are caused by 
insufficiency of elements in the soil that had not hitherto been suspected 
of being of importance in plant nutrition. Warrington ” and Brenchley ™ 
startled the botanical world some years ago by demonstrating that boron 
was an essential element in the proper nutrition of certain green plants. 
Since then Brandenburg * has suggested that boron-deficiency in the soil 
is the cause of the serious ‘ heart-rot ’ disease of sugar beet and mangolds. 
Another element having the property—formerly unsuspected—of exer- 
cising an important réle in the nutrition of some plants is manganese. It 
has long been known that oats did not thrive on certain soils unless salts 
of manganese were added. On such land the oats were stunted in growth, 
the leaves were affected by grey blotches, and the plants died prematurely, 
the disease being known as ‘ grey leaf’ or ‘ grey-speck.’ Small amounts of 
manganese sulphate applied to the soil enabled a healthy crop to be grown. 
Samuel and Piper 7* have shewn by careful experiments that minute quan- 
tities of manganese must be available in the soil to allow of the normal nutri- 
tion of oats and certain other plants. Sucha disease as that of “ grey leaf ’ of 
oats is now known as a ‘ manganese deficiency’ disease. Another inter- 
esting example of the importance of nutritional factors in the maintenance 
of well-being in crop plants is afforded by the researches of Storey and 
Leach 77 on a grave disease of tea bushes in Nyasaland, which causes 
chlorosis and rapid death. They have demonstrated that this disease is 
73 Ann. Bot., 87, p. 629 (1923). 
74 Ann. Bot., 41, p. 167 (1927). 
75 Phytopath. Zeitschrift, 8, p. 499 (1931). 
76 Ann. App. Biol., 16, p. 493 (1929). 
77 Ann. App. Biol., 20, p. 23 (1933). 
