TUBERCULAR SWELLINGS ON THE ROOTS OE VICIA EABA. 
557 
Water ...... 1000 c. cm. 
KNOg. 1 grm. 
NaCl. 0-5 „ 
CaSO*. 0-5 „ 
MgS0 4 . 0-5 „ 
Ca 3 (P0 4 ) 2 ..... 0-5 „ 
The seedlings were placed in a slit cork, so arranged that the whole of the root was 
submerged in the solution, and that the shoot could grow up freely into the light 
and air, which, together with the temperature and other conditions, were carefully 
regulated. 
I followed Sachs’ plan also in placing the cultures in new solutions when necessary, 
and in some cases of allowing their roots to remain for some hours in a solution of 
gypsum or salt between the changes. However, these precautions are scarcely needed 
if the roots are kept darkened and the solution changed once a fortnight or so. In 
cases where chlorosis was beginning to set in, traces of a salt of iron were added 
as necessary. 
It may remove all cause for doubt to state that it is just as easy to obtain the 
tubercles in the roots of these water-cultures as it is on the roots of the plants growing 
in soil, in pots, or in the open; and, conversely, it is in both cases possible to prevent 
their formation by removing the infecting germs (by heating the medium, &c.). 
There are in my greenhouse and laboratory at the present hour no less than 
32 water-cultures and 26 cultures in pots, growing under conditions so well controlled 
that it is possible to predict with great accuracy when and where tubercles will be 
developed. 
I will confine myself to the following inferences from my Table of 81 experiments 
made this year, merely reserving the opinion that the ambiguous results in six or 
seven cases were due to faulty sterilisation. 
The chief points to notice are (1) the all but invariable development of the tubercles 
within a month, when the Beans were germinated in sand or soil not previously heated; 
(2) their non-development when the medium was sterilised by being heated ; 
(3) the number of times I succeeded in infecting the roots by means of pieces of old 
tubercles placed among the root-hairs; and (4) the number of times the infecting 
hypha was discovered entering the cortex by means of the root-hairs. 
It is partly on these grounds that I infer that the tubercles so common on the roots 
of the Bean are due to the action of the Fungus, the very minute germs of which are 
all but universally distributed in the soil; and it will be conceded that there is 
evidence for believing that germ to be the gemmule developed in the cells of the 
tubercle. The further physiological effects of the symbiosis must be reserved for 
future discussion. 
