458 Philippine Journal of Science 1920 
over thirty years later that Lehmann ® published an account of 
experiments which seemed to show that ammonium sulphate 
may be a source of nitrogen for certain higher plants. He 
employed solution cultures and supplied all the necessary ele- 
ments in all cases, but some cultures were furnished with 
nitrogen as a nitrate (calcium nitrate), while the nitrogen of 
_ others was supplied as an ammonium salt (ammonium sulphate). 
He observed that maize plants developed normally for forty- 
one days (from the seed) in solutions containing ammonium 
sulphate, while the plants with calcium nitrate showed only poor 
growth during that period. After this first period of forty-one 
days, however, his “nitrate” plants recovered and continued 
with good growth, while his “ammonium” plants became chlo- 
rotic and sickly. Also, Lehmann observed that the chlorotic 
plants of his nitrate group within the first forty-one day period 
might be made to assume normal growth and appearance, if they 
were transplanted to a culture solution containing ammonium 
sulphate; in two days they became green. Furthermore, when 
healthy plants of his ammonium group were similarly trans- 
planted to a solution containing sodium nitrate, they soon be- 
came pale and sickly. 
The same author obtained similar results with tobacco plants 
grown in sand cultures. He supplied the necessary minerals, 
furnishing nitrogen either as ammonium sulphate or as sodium 
nitrate. The plants grown in the medium containing ammonium 
sulphate were healthy and grew normally from the beginning 
to the end of the experiment. Those supplied with nitrogen 
as sodium nitrate were chlorotic and unhealthy during the first 
half of the vegetative period, but they afterwards became green 
and vigorous, although the final yield was much lower than that 
obtained from the cultures with ammonium sulphate as the 
source of nitrogen. : 
Lupine plants grown in sand cultures in Lehmann’s exper! 
ments gave better vegetative growth when nitrogen was SUP 
plied as sodium nitrate than when it was furnished as ammonium 
sulphate, but the yield of seed was larger in the latter case. 
From these studies Lehmann came to the conclusion that 
some plants require nitrate nitrogen, others require ammoniaca 
nitrogen, and still others require one of these two forms of 
nitrogen during the early stages of growth and the other form 
during the later stages. While the experimentation on which 
* Lehmann, Jul., Ueber die zur Ernahrung der Pflanzen geeignets® 
Form des Stickstoffes, Biedermann’s Centralbl. Agr.-Chem. 7 (1875) 403-409. 
