ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 503 



of the typhoid-dysentery group were used principally, and all possible 

 sources of contamination were rigorously excluded. By using broth 

 + 20 to phenolphthalein, and by sub-culture from this to agar or to 

 MacConkey's medium, thence back again to ordinary broth + 10 to 

 phenolphthalein, a great increase in the size of the organisms is 

 obtained, but the bacilli still give the classical cultural, fermentative 

 and serological reactions. 



In all the broth cultures studied, reproduction by simple binary 

 fission was still the predominant feature, and in studying the " aberrant " 

 types of reproduction of single living organisms on the warm-stage on 

 solid media, such as gelatin-agar, ordinary binary transverse fission was 

 found to hold the field mainly, though not absolutely to the exclusion of 

 other forms of reproduction. Reproduction by gemmation occurs freely, 

 in conjunction with ordinary binary fission, only so long as growth 

 proceeds in the thin layer of broth on the cover-slip, and largely comes to 

 an end when colonies are beginning to form on the solid medium. Some 

 of the buds observed were very minute, and when examined by the dark- 

 ground illumination method were found to be minute bacilli undergoing 

 binary fission. Not unf requently these appear as coccoid bodies if binary 

 fission has not begnn. The presence of these minute forms is probably 

 the explanation of the apparent filterability through Chamberland filters 

 of such relatively large organisms as Bacillus hronchisepticus, and is 

 perhaps responsible for the general view that even well-made Berkefeld 

 filters are not suitable for bacteriological work. 



Bacteriology in Plant Pathology."' — F. L. Stevens gives an 

 interesting account of recent advances in the study of plant pathology. 

 " It appears that the bacteria involved in plant disease are pre-eminently 

 of the genera Pseudomonas and Bacillus. The Cocci, Bacteria and 

 Spirilli, so prominent in animal pathology, sink to a very minor position." 

 Some of the more important organisms are included in the following list : — 



Bacillus amyloverus (host. Pomes), the cause of the pome blight, is 

 widespread and the cause of immense pecuniary loss. 



Fseuclomonas radiciclea (host. Legumes) occupies the anomalous 

 position of being a beneficial disease. 



P. solanacearum (host, Solanaceae) is very wide-spread and destructive, 

 as are also P. camprestris (host, Crucifers) and B. tracheiphilus (host, 

 Curcurbs). B. carotovorus is the cause of soft rot of parenchyma on 

 many hosts and the loss of much produce during storage. 



The bacterial leaf-galls of the Rubiacese, originally described by 

 Zimmermann, are of particular interest as possibly cases of symbiosis 

 rather than parasitism. 



P. tumefaciens, the cause of crown-gall on numerous hosts, has been 

 shown to furnish an example of an unsuspected type of plant disease, 

 in many respects analogous to human cancer. 



B. ave?ise with P. avenae (host, Oats) present an unique case of 

 symbiosis, in that the latter organism is, according to the work of 

 Manns, much more productive of disease when accompanied by the 

 former organism. 



* Trans. Amer. Micr, Soc, xxxvi. (1917) pp. 1-12 {1 chart). 



