292 The Botanical Gazette. {July, 
takes place transversely, and this produces an elongated 
growth although lateral protuberances often arise making a 
branched and irregular appearance. They liken the swollen 
branched bacteroids to a gill respiration, the nitrogen being 
absorbed by the water and this coming to the absorbing sur- 
faces in a dissolved condition. The fact that nodules are 
less active in their assimilatory Capacity in water cultures 
than in soil is commented upon and the inference drawn that 
the slower exchange of gases in the water than in capillary 
soil is the cause of this lessened activity. 
Variety of species of nodule-producing organism. 
Regarding the question as to whether there is a variety of 
species of the nodule forming organisms, Nobbe and Hiltner 
give some additional experiments in infecting different legumes 
with bacteria normally found in other species.** In nitrogen- 
free soils, certain plants like Lupinus luteus, L. augustifoltus, 
Acacia Lophantha and A. ¥ulibrissin produced tubercles when 
inoculated with bacteria of pea and bean tubercles. In sol 
containing nitrogen no infection could be noted, indicating 
that there must be a nitrogen hunger in the plant before the 
tubercle bacteria of one species of legume can penetrate a 
root system of another species. 
Atkinson?‘ records in his paper the failure to produce tuber- 
cles on Dolichos sinensis when inoculated with pure cultures 
isolated from Vicza sativa while this organism introduced into 
its normal host developed abundant tubercles. 
The multiplicity of forms that have been noted among ; 
bacteroids of different legume species has led to the vier 
there are specific forms for different species of legumes. . 
view receives support from a morphological basis but the ia 
certainty of a classification based upon a possible involutio 
or abnormal structure is obvious. he 
Schneider?® classified the tubercle organisms under ae 
generic title of Rhizobium, adopting Frank’s generic ere 
He based this classification at first on purely morphologi< 
characters as they appeared in the living tubercle, but he 
since cultivated several forms artificially and has a 
tural characteristics to his morphological data. 
the 
?8 For earlier data on this question see Landw. Vers. Stat. 39: 227-359: 
24 Bot. Gaz. 18: 157. 1893. 
”° Ber. d. d. bot. Ges. 12: 11. 1894. 
1893 
dded cul- : 2 
