132 NATURAL SCIENCE. Feb , 



attack the starchy stores of reserve-material or the sugary fruits of 

 the hosts, and it is precisely here that, as has been mentioned above 

 in the case of fungi, thin partitions divide the saprophyte from the 

 parasite. On the other hand, there are cases, like the blight on oats, 

 where all parts of the young plants are affected, and, in short, there is 

 a pleasing variety in the organs attacked. I am far from denying all 

 these cases, but in matters of this kind it is, above all, necessary to 

 " prove all things," and I prefer to retain, at all events in some cases, 

 a " skeptical " attitude, especially as the data we possess are 

 " meager." Not so, however, with Dr. Russell's own experiments, 

 which are a valuable contribution to the literature of the subject, 

 and a most promising performance. Some of his statements are 

 open to comment, if not to criticism, on minor points, but this is 

 hardly the place for a discussion of methods, etc., and the whole 

 thing is so interesting a study in immunity that I summarise his 

 conclusions. " The artificial inoculation of higher plants with 

 different micro-organisms (not known to be pathogenic for plants) 

 reveals the fact, contrary to the usually-accepted idea, that quite a 

 goodly number of different species are able to withstand the action 

 of the living plant organism for a not inconsiderable length of time." 

 Of these he finds saprophytes particularly prominent — but not all 

 equally so. Facultative parasites on the animal body were not found 

 to be adapted to live in plant tissue, with the exception oi B . pyocyaneus 

 and the Schweineseuche Bacillus. "The inoculation of plants, not 

 taxonomically related to the natural hosts of bacterial plant parasites, 

 with species of micro-organisms naturally parasitic on vegetable 

 tissue, showed that while the bacteria were unable to spread, they 

 could survive at the inoculation point in large numbers. . . . Not 

 only were numbers of different species of bacteria able to live in the 

 plant from 40 to 80 days or more, but many of them (mostly sapro- 

 phytes) were able to spread throughout the tissue of the plant to a 

 limited extent (20 to 50 mm. or more)." This spreading was 

 generally intracellular, not intercellular, and always in an upward 

 direction. Dr. Russell thinks that this was not owing to the 

 transpiration stream, but to the actual growth of the micro-organism. 

 In the case of bacteria entering by wounds, he thinks it possible 

 that they could enter through lesions so small as to escape notice, 

 and that they might even live in the tissue after the wound has 

 healed over. "In the case of parasitic species on plants, they some- 

 times effect an entrance into tissues without the intervention of 

 wounds of any sort." The exemption of plants from bacteria in 

 general, he distinguishes as resistance ; while he reserves the term 

 immunity for "the ability of a certain group of plants to be refractory 

 towards a disease germ that is able to cause a pathological condition 

 in closely-allied forms of plant life." This certainly seems an unneces- 

 sary distinction, because it is scarcely possible in any case to draw 

 the line for immunity unless one is a "harbitrary gent," though the 



