112 
Journal of A gricultural Research voi. xxvii, no. * 
modification of the basic solution which contained no added ions of 
direct value. Two further modifications were prepared, one containing 
0.0171 gram-molecules of CaCl 2 per liter, the other an equivalent quantity 
of MgCl 2 . Eleven different solutions were used in all, each applied to 
four crocks. 
The nutrient solution was renewed at intervals of three weeks by 
opening the drain at the bottom of the crock and flushing the sand with 
fresh solution. When the solution ceased to drain from the openings 
the crocks were weighed for a new base weight. As in all cases the 
amount of solution retained approximated the maximum water capacity 
of the soil, the successive base weights were in fairly close agreement. 
The plants were grown from November to June. The long growth 
period and slow development during the winter resulted in a high water 
requirement as compared with field-grown plants. It was March before 
heading began and the end of May before the majority of the plants 
were ripe. It appears that length of day is an important factor in con¬ 
ditioning the time of maturity of greenhouse-grown wheat. It was 
necessary to cut the plants before all of them, particularly those in the 
excess N and K series, were fully ripe: the data from these are not 
considered in the summary, but a majority of the plants had plump 
hard grain at this time. The yield was rather below that of field-grown 
plants, the average for the three series of stem rust, leaf rust, and control 
plants translated into terms of bushels per acre being 9.6, 9.1, and 11.5, 
respectively. Certain cultures (four crocks), however, yielded at the rate 
of 20 to 25 bushels per acre and the best individual plant on a similar 
basis yielded 34 bushels per acre. 
Three series of crocks were treated with each of the 11 culture solutions. 
One of these was left uninoculated as a control; in the second and third 
infection by stem rust and by leaf rust, respectively, was produced by 
artificial inoculation. Leaf-rust infection was readily obtained by atom¬ 
izing the plants with a water suspension of urediniospores, but this 
method was unsuccessful with stem rust. With the latter, initial infec¬ 
tions were produced by moistening the leaves and then applying dry 
urediniospores, following which steam was allowed to escape into the 
house for 48 hours while the ventilator remained open. In this way a 
nearly saturated atmosphere and dense fog could be maintained for two 
days at a time, resulting in copious precipitation of dew on the foliage. 
This process was repeated at monthly intervals to simulate the succession 
of new infections that occurs in the field. By these means a severe 
epiphytotic of stem rust was maintained, and a lighter one of leaf rust, 
during more than half of the growth period. In each case fairly uniform 
infection was produced on the replicate crocks of a culture, although 
some diversity in this respect could not be avoided. 
The quantity of rust was estimated at the time of heading according 
to the rust scale of the Office of Cereal Investigations; but it is to be 
noted that at this time the amount of leaf rust was less than it had been 
at an earlier stage, while the stem rust was at a maximum. At maturity 
the tops were cut at the soil level, dried for two days at 105° C., and 
weighed. The grain was then hand threshed, dried again, and weighed. 
The data for the various cultures in each series are presented in Tables 
II and III. A direct comparison is thus permitted of a set of plants free 
from rust with a set each of leaf-rusted and stem-rusted plants which 
grew under identical conditions. Since there were only four plants in 
