196 Spratt. — A Comparative Account of the 
direction of the length of the nodule, become multinucleate, and later the 
nuclei disappear. Many empty nodules were also found on the roots, in- 
dicating that they only last for a limited period which does not correspond 
with the life of the root as in non-leguminous nodules. This type may be 
called the Mimosoideae type. 
The amount of nitrogen which is fixed by Bacillus I'adicicola has been 
thought to be connected with the quantity of slime which is produced 
under the given circumstances. When the development of slime is large 
the bacteria are held in it and form what is called a zoogleal thread. It is 
in this form that they are very active in entering the root-hairs and passing 
from cell to cell of the nodule. In the Viceae type the zooglea persists 
much longer than in the other groups in the cell of the nodule itself. 
Eventually the slime is absorbed and the bacteria live freely in the cell, 
then in many cases they no longer remain rod-shaped but assume a 
characteristic form, e. g. in Vida Fab a they become V and Y shape, in Lotus 
corniculatus spherical. These have been called bacteroids. Buchanan has 
described a large number of these forms both in nodules and artificial 
cultures and ascertained that their production and formation depend very 
largely on their nutrition. Many have believed them to be absorbed 
by the plant, but inside them are small denser spherical bodies, the presence 
of which renders the organism much more resistant to its environment than 
it was before, consequently they are more and more abundant as the nodule 
grows older and the season advances. 
The nuclear changes which have been observed above are associated 
with the presence of the zooglea. It is in those cells in which the zooglea 
persists and envelops the nuclei that the latter become amoeboid and 
divide amitotically before the cell becomes a permanent cell with very little 
protoplasmic content at all. This has also been recorded in non-legumin- 
ous nodules ; e. g. in the Podocarpineae and Elaeagnaceae the nuclei behave 
as , described above for the Viceae type, but have not been observed to do 
so in Alnus , although it is so much like Elaeagnus in other respects. 
The presence of the zooglea apparently has a stimulating effect upon the 
nucleus. 
In artificial cultivation it has been observed that the amount of slime 
produced is largely influenced by the medium used, e. g. the kind of carbo- 
hydrate supplied. Bacteria obtained from nodules of different plants also 
behave rather differently towards the carbohydrate supplied, some respond- 
ing more readily to maltose, others to sucrose, and so on. They all can 
utilize a very large number of carbohydrates, but become particularly 
adapted to one form, probably by growing in the root of a plant which 
contains that one. Buchanan found the production of gum or slime in 
some cases was favoured by the presence of sodium succinate, ammonium 
citrate, glycerine, glucosides, and inhibited by asparagin, whilst in other cases 
