22 AMERICAN JOURNAL OF BOTANY [Vol. 8 
9B. Same nitrogen source, medium with i percent mannite 
No. 
Culture 
Species 
Growth 
Total Mg. 
N Found 
Weight of 
IVIedium 
Grams 
Mg. N per 
100 Gr. Average 
Medium 
Mg. Loss 
or Gain, 
100 Gr. 
Check 
Ster. 
27.86s 
14.8 75; 
18.733 ' 
Check 
Ster. 
14.8 'J'^ 
17.071 
■ 17.728 
Check 
Con.* 
25.826 
148.60 
17.380 
I 
ChlorellcL vulgaris 
+ + + 
22.818 
148.70 
15-345 ' 
I 
Beyr. 
+ + + 
2'^,SS8 
14.8 00 
15.821 
15.280 
I 
+ + + 
2I.70Q 
14-8. 
14.675 
2 
Stichococcus sp. 
+ + + 
2 1 .QOd 
14.8 70 
14-730' 
2 
2J. I 
148.70 
16.349 
> 16.529 
— T TOO 
2 
+ + 
14.8 6'; 
18.507 
5 
Chlorella (?) sp. 
+ + 
26 07^ 
148.60 
I8.I5I 1 
5 
+ + 
27.029 
i48!6o 
18.189 
> 17.764 
+0.036 
5 
+ + 
25.189 
148.60 
16.951 , 
6 
Scenedesmus (?) sp. 
+ + 
19-634 
148.55 
13.217 ^ 
6 
+ + 
24.326 
148.65 
16.365 
> 15.603 
-2.125 
6 
+ + 
25.609 
148.65 
17.228 ^ 
1 1 
Chlorella (?) sp. 
~ 1 r 
148.70 
9.066 ' 
II 
+ + + 
Lost 
148.80 
^ 9-430 
-8.298 
II 
+ + + 
14.613 
149.20 
9-794 , 
7 
Protococcus sp. 
+ 
22.251 
149.20 
14.914 
> 14.914 
7 
+ 
Lost 
149.15 
-2.814 
3 
Protosiphon 
+ + + 
24.481 
149-15 
16.414 \ 
3 
botryoides 
+ + + 
26.293 
148.45 
17.712 j 
17.063 
-0.665 
Average all cul- 
tures (omitting 
species no. 11) 
16.192 
-1.536 
Discussion 
From a study of the foregoing tables it is apparent at once that sub- 
stantial increases in the total combined nitrogen content of the culture flasks 
occurred with the media containing nitrate nitrogen and glucose. Fixation 
on these media was not confined to any one species, most of the forms used 
showing the ability to utilize the uncombined nitrogen of the air. The 
cases of Protococcus (species no. 7) and Protosiphon (species no. 3) may be 
questioned, but it will be noticed that of all the species grown on ammonium 
nitrate with glucose in the 1 91 9 experiment (table 8 A) Protococcus gave the 
highest gain in nitrogen, and that in the same experiment Protosiphon gave 
an increase of nearly 2 mg. on calcium nitrate with glucose (table 9A). 
Although an increase of only 2 mg. is a small amount to base definite 
conclusions upon, the evidence is certainly in favor of the assumption that 
these two species also possess the ability to fix nitrogen. As regards 
species nos. i, 2, 5, and 6 there can be no question about their ability to 
fix nitrogen, since the increases with these species range from a fraction 
of a milligram to over 8 mg. per 100 grams medium, representing additions 
to the total nitrogen content of the flasks of from i to 51 percent. The 
highest increase noted was in the case of one of the cultures of species no. 5 
on calcium nitrate with glucose, in the 1919 experiment (table 9A); this 
flask showed a total gain of 12.53 mg. over the average of the checks, an 
