64 CAUSE AND NATURE OF CROWN-GALL 



Flemming and stained in the usual way, the work admits of 

 comparison. Both diseases being evidently caused by. slime- 

 molds, one woukl expect somewhat similar effects upon the tis- 

 sues of the respective host plants and some similarity, at least, 

 between the plasmodial stages of the parasites. 



The following are some important similarities that maybe 

 noted : 



i. Both parasites induce acceleration of growth and cause 

 large galls of hypertrophied tissue on their respective hosts. 



2. The cells infected by both parasites are almost instantly 

 blackened by osmic acid. 



3. Vast numbers of small, spherical black bodies in both in- 

 stances appear in the diseased tissue when fixed in Flemming. 



4. Both parasites appear in their respective hosts as densely 

 filling certain cells with frothy, vacuolar protoplasm. 



5. Amoeboid bodies are present in certain phases of the vege- 

 tative development of both parasites. 



6. Both parasites consume the cytoplasm of the host cell and 

 finally the nucleus. 



7. The first visible effect of the parasites on the nuclei of 

 their respective hosts is to cause them to enlarge and assume 

 various abnormal forms. 



8. In both diseases many " erythrophyllar " bodies appear 

 in the diseased nuclei when fixed and stained. 



In 1892 Hermann Miiller-Thurgau published a short account 

 of a slime-mold as causing galls on the roots of the pear." I 

 was unable to procure a copy of the publication containing this 

 account and until the completion of my studies was unaware of 

 its existence. At the last moment, however, I received a letter 

 from the author inclosing a typewritten copy of this article. 

 It is a brief notice of the microscopical examination of galls 

 from the roots of the pear and an account of the finding of a 

 mvxomycete in the large parenchyma cells of the hypertrophied 

 tissue. Small spherical bodies were also found in some cells 

 which were thought to be spores. 



43 Miiller-Thurgau, Hermann. — Em Schleimpilz bei den Wurzelkropf 

 der Birnen. Jahresbericht der Deutschschweizerischen Versuchsstation 

 und Schule fiir Obst-, Wein-, und Gartenbau in Wadensweil, II (1891- 

 1892). 



