8 
AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
Method of Recording Growth. — Records of the growth of the cultures 
were made at intervals of three or four weeks. These consisted of written 
notes comparing the development of the different species on the same 
medium, and the difference in amount of growth of the same species on the 
ten different media. Charts were also prepared at about monthly intervals 
showing the growth in each culture flask by means of colored crayons. 
These were found very helpful in making growth comparisons, as they 
present to the eye at once the relative development in every flask. 
Since it was the plan of the experiments to analyze the entire contents 
of the culture flasks at the end of the growing period, it was not found 
advisable to attempt any actual weight determinations of the ''crop" 
produced on the various media by the different species. Experiments with 
solution cultures are in progress now from which it is hoped some accurate 
data may be secured, showing the actual amounts of growth produced on 
different media and what relation the dry weight of algal material produced 
bears to free nitrogen assimilation. From a comparison of the written 
notes and colored charts, however, the following general statements may 
be made. 
igiy-i8 Experiment. — In this experiment there was a remarkable sim- 
ilarity in the amount of development of all four species on any one of the 
media used. Only in a few cases did there appear to be any marked specific 
differences in the reactions of the organisms to the medium. In general, the 
presence of glucose resulted in a vigorous and rapid development of all 
species, irrespective of the nitrogen source. 
Series i-j. The relative growth of all the cultures is indicated in the 
tables which follow, by means of plus signs. Since no fixation occurred in 
the series in which the nitrogen was supplied as ammonium sulphate or in 
the organic forms used, the detailed observations of these series are omitted. 
The results on the nitrate media, however, were so striking that a more 
detailed account of the growth on these media is here presented. 
Series 4 (ammonium nitrate, without glucQse). Growth was slow but 
steady in all cases. Species nos. i, 5, and 6 continued healthy to the last, 
giving "very fair" growths. The growth of species no. 2 was "fair," 
but the cultures were dead at the end of the experiment. 
Series 4A (ammonium nitrate, with i percent glucose). All species 
started with very vigorous growths, the effect of the presence of glucose 
being very evident. Species no. i produced a "luxuriant" growth at first, 
but after three months began to deteriorate, turning brown over most of 
the surface. Before growth had completely ceased, however, both cultures 
of this species began to revive, and by the end of the fourth month were 
again bright green. The cultures then, slowly waned a second time, only 
small portions remaining green at the end of the experiment. Species 
nos. 2, 5, and 6 grew steadily from the start and remained healthy, no. 2 
producing a "luxuriant" growth and nos. 5 and 6 "very good" growths. 
