AN anatomist's VIEW OF VIRUS DISEASES 79 



Considering the history of the anatomy of disturbed or deranged plants, 

 the so-called pathological anatomy, we find that pertinent information was 

 compiled in 1909 by Sorauer, then, more comprehensively, in 1925 by 

 Kiister, both German botanists. Kiister's work was a milestone in that it 

 not only assembled the information in orderly fashion but also crystallized 

 the terminology with regard to the pathological anatomy of plants. There is, 

 as a result, a rather general agreement on such terms as hypertrophy and 

 hyperplasia, referring to phenomena of abnormally intensified growth and 

 differentiation, and hypoplasia, denoting inhibition of growth and differen- 

 tiation. Commonly hypertrophy is used to designate an excessive enlarge- 

 ment of a cell or a part of it; hyperplasia, an excessive multiplication of 

 cells. In contrast, we use only one term, hypoplasia, to denote inhibition of 

 development, be it expressed in too small a size of cells or cell parts, or too 

 small a number of cells or cell parts, or nondevelopment of some features 

 that are normally expected to be present in the cell or tissue at the particular 

 stage of their development. Death of cells and tissues is referred to as necro- 

 sis, with necrotic as the adjectival form. 



A review in the English language of some of the general aspects of patho- 

 logical anatomy — or morbid anatomy, as the author called it — was written 

 by Butler in 1930. He paid particular attention to the fungal and bacterial 

 diseases. Otherwise the information on the anatomic effects of fungi and 

 bacteria must be sought in various compendia and special articles dealing 

 with the diseases induced by these causal agents. A considerable volume of 

 literature in pathological anatomy deals with the very interesting and highly 

 complex plant galls, mainly those induced by insect stimulation. 



Viruses were recognized later than fungi and bacteria as causal agents 

 of plant diseases, and the first comprehensive review on the structural effects 

 of the viruses upon plants appeared in 1938 (Esau, 1938). Workers of vari- 

 ous countries have studied virus diseases and, incidentally, described the 

 internal symptoms, but mostly those in plants in which the disease had be- 

 come well established. The ontogenetic, or developmental, approach to the 

 studies of the anatomy of virus-diseased plants and the extensive inquiry 

 into the biologic relation between viruses and the tissues of the host are 

 developments that resulted in a large measure from work in the United States 

 (see Bennett, 1940b, 1956; Esau, 1938, 1948b). 



Anatomic changes induced by plant viruses. Plants react with cer- 

 tain fundamental changes in structure in response to a variety of injurious or 

 noninjurious stimuli. In this respect, reactions to viruses are not exceptional, 

 and we find, in virus-diseased plants, such basic pathologic symptoms as 

 hypertrophy, hyperplasia, hypoplasia, and necrosis, often in combinations of 

 two or more. An enlightening aspect of viral effects is that the symptoms in- 

 duced by different viruses differ with regard to their distribution in the plant. 

 Anatomic studies have proved to be particularly useful for the recognition 



