TUBERCULAR SWELLINGS ON THE ROOTS OP VICIA PABA. 
543 
results were only obtained recently. The chief investigation lias been almost entirely 
confined to tlie tubercles on Vida Faba (JL), the common Broad Bean, no particular 
regard being paid to the garden varieties employed. 
At the same time it should be stated that I have seen and to a certain extent 
examined them on the roots of several Clovers,* Peas, Vetches, and the Scarlet 
Runner in this country, on Broad Beans in Germany, and on the roots of several 
Papilionacese in Ceylon, and can to a certain extent confirm the much more extensive 
observations of Frank as to their ubiquity and general resemblance. In Manchester 
it was by no means rare to find the tubercles on the roots of Vida Faba as large as a 
small Hazel-nut, and I have had specimens even larger from the damp heavy soil of 
some districts. In the light sandy soil of this part of Surrey I have not seen them 
much larger than a fair-sized pea, though they are often very numerous and crowded 
on the roots. 
I have examined many hundreds of roots of Vida Faba during the last four years, 
and have only once or twice failed to find the tubercles on plants in fruit, and even in 
the case of younger plants the percentage of failures has been small. 
In 1884, at the Owens College, Manchester, several beans grown in pots of burnt 
soil, and watered with solutions of nutritive salts, developed no tubercles on the 
roots; and in the majority of cases, then and since, beans grown for laboratory 
purposes in carefully-prepared nutritive solutions have been devoid of the tubercles. 
Nevertheless, this has not always happened, and in some instances the water-cultures 
have developed excellent specimens of the tubercles. Considering that these were 
growing in solutions of chemically pure salts in distilled water,t it is hardly to be 
wondered at if one sometimes doubted the existence of an external cause for the 
swellings, and felt tempted to believe that either the tubercles were really due to the 
roots themselves, or that if a parasite exists it is present in the seed from the first. 
The possible sources of infection in these experiments were (l) germs in the air, 
(2) germs attached to the testa of the Bean, (3) the medium (damp sand or sawdust) 
in which germination was commenced. Although it was not demonstrated, I thought 
the second a more probable source of error than the others. I have this year found 
the tubercles on a bean which was germinated in “ clean river-sand ” not heated, and 
then grown as a water-culture—everything hereafter chemically pure, and in a new 
building. Of course it is not impossible that a germ might fall into the culture ; but 
it seems much more likely that the infecting agent was attached to the seedling 
before its roots were placed in the solution of nutritive salts, and possibly came from 
the sand. In any case, whether the cause of infection is in the medium or on the 
Bean, it must be very minute and ubiquitous, and the results quite bear out Frank’s 
comparison with the minuteness and ubiquity of putrefactive and yeast germs. In 
* Those of the Lupin may be distinct. 
f It should be stated that they were exposed to the air, however, and that no regard was then paid to 
the medium in which they were allowed to commence to germinate. 
