IOWA ACADEMY OF SCIENCE 
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series. At no time have the minerals given as good growth as the manure, and 
in the earlier trials the amount of soluble plant food was much in favor of the 
mineral fertilizers. The pictures show something in addition, and that is, that 
the manure helped the clover immediately and some time before the minerals 
helped it. Therfore if the green weight had been taken earlier, the difference 
would have been greater. With all this evidence it is certain that manure 
has some constituent that helps the growth of clover, other than the nitrogen, 
potassium and phosphorus found in it. 
The question now is, what is this constituent of manure? It has been shown 
that the manure did not correct acidity of the soil, that the physical effect of 
the manure is not a help to the clover, and further, that it was not on account 
of the bacteriological relations. There seems to be only two possible explana- 
tions left. One is that the soluble organic matter in the manure is used as 
such directly by the clover plant for nourishment, without first being broken 
down and then assimilated in simple forms. The second is that there is a 
poison in the soil and that the manure neutralizes it. The one is the 
toxin theory, the other the soluble plant food theory. At this time the plant 
food question will be discussed, leaving the other to be considered by itself. 
There have been a few investigations that throw some light on the question 
of the ability of plants to use organic matter as food. L. Lutz has reported 
considerable work in Bulletin de la Societe Botanique de France. Abstracts of 
these papers have appeared in the Experiment Station Record from time to 
time.^ 
Lutz has found that various nitrogen compounds can be assimilated directly 
by plants. He has done a vast amount of experimenting, using flowering plants, 
algae, fungi and molds, and has tested them with a great number of nitrogenous 
compounds. He uses a sterile medium, sand or similar culture, and for each 
kind of plant the only source of nitrogen was to be found in the compound 
under investigation. Experiments are reported with cucurbit seedlings, in 
solutions containing leucin and tyrosin as the only sources of nitrogen. Where 
leucin was added to the culture medium, gains of 35.8 per cent to 40.8 per cent 
in nitrogen are reported, while for tyrosin a gain of 11.9 per cent is given. 
Leucin being more soluable is much better assimilated than tyrosin. 
Leucin contains the radicle NH 2 . It occurs in different animal fluids and is 
physiologically very important. It is formed by the decay of albuminoids and 
is soluble in 48 part of water. Tyrosin is quite similar. 
The results, the author claims, have a practical bearing in the practice of 
composting. In this way the frequently rapid action of manures may be ex- 
plained. The author believes it is practically demonstrated that many organic 
nitrogenous substances are directly assimilated by plants, and the common 
belief that ammoniacal fermentation takes place first, followed by nitric fer- 
mentation, is not in accord with what actually occurs in the plant. 
What about the assimilation of carbohydrates by plants? M. Molliard^ of 
France experimented with radishes, one lot being grown in mineral solutions, 
the other in various forms of carbohydrates. When grown in solutions of 
saccharose, glocuse, levulose, dextrin, etc., the color, size, form and structure 
of the leaves were greatly modified. The plants were able to make consider- 
able growth, utilizing the carbohydrates through their roots. 
^Exp. Sta. Rec. XVIII, p. 348. This gives previous references. 
•■^Exp. Sta. Rec. XVIII, pp. 25 and 127. 
