388 Notes. 
July 2i. examined four, all free from tubercle. 
„ 25. added 10 grams KN 0 3 . 
„ 28. examined four plants, one with tubercle. 
Aug. 1. added 10 grams KN 0 3 . 
„ 4. examined twelve plants, three with tubercle (on youngest 
roots). 
„ 8. added 10 grams KN 0 3 . 
„ 11. examined fifteen plants, four with tubercle. 
Summary. 36 plants were grown from the 50 seeds, and of these 
8 produced tubercles. 
Remarks. The results of all these experiments agree in showing 
that the development of tubercles is much less when nitrate is present 
in the soil than when it is absent. It is also indicated that as the 
amount of nitrate diminishes, the development of tubercles becomes 
more marked. In experiments I and II, the tubercles were first 
detected nine days after the last supply of nitrate ; the soil having 
become in the meantime impoverished in nitrate by watering 
(Experiment I) or by rain (Experiment II). In Experiment III, 
although the supply of nitrate was continued to the last, the gradual 
development of tubercles may be accounted for by the exceptionally 
rainy season, in consequence of which the soil was impoverished 
very rapidly. In all cases in which tubercles made their appearance 
on the roots of plants which had been supplied with nitrate, they are 
exclusively developed on the youngest roots, especially on those near 
the surface of the sand ; in that part of the soil, that is, which would 
naturally lose its nitrate most rapidly. 
A remarkable fact is that noted in Experiment I, on May 5 ; 
the absence of tubercle in ten plants which had received no nitrate. 
As no parallel case occurred in Experiment II, in which the plants 
were fully exposed to the sun, it appears that the absence of tubercles 
in these plants is to be connected with their imperfect exposure to 
light. It may be that tubercle is only produced when the conditions 
of nutrition are highly favourable ; that the development of tubercle is, 
in fact, intimately connected with the metabolic activity of the plant. 
The special object of Experiment III was to investigate the possibly 
infective origin of tubercle. The sand in box B had contained during 
Experiment II forty-seven tuberculous plants ; yet, in Experiment III, 
only eight plants out of thirty-six grown in the same sand were 
tuberculous. This experiment does not conclusively prove that 
