no 
Journal of Agricultural Research voi. xxvii, no. » 
Wimmer (23) showed that the water requirement of sugar beets and 
celery is increased by nematode infection, and believed this to be due to 
the slower growth of such plants. It is well known that the “compound 
interest law of plant growth” ( 1 ) falls far short of realization when 
growth is abnormally slow, and lowered water economy results also. 
That parasitic fungi may affect the water relations of the host in other 
ways than by mechanical rupture of the tissues which normally protect 
the transpiring tissues, or by causing less economical use of water owing 
to retarded growth, is evident from the work of Haskell (9), who showed 
that in Fusarium wilt of potatoes, either the destruction of roots or the 
production of toxic excretory products by the fungus may be responsible 
for wilting of the plant, but mechanical stoppage of the vessels does 
not occur. The effect on water requirement is unknown. 
Fungous infection may result either in acceleration or diminution of 
transpiration. The character and intensity of the effect are determined 
by the mechanical rupture of protective tissues, by local necrosis of the 
epidermis or mesophyll, or by toxic excretions, all of which result in 
accelerated water loss. On the other hand, transpiration may be dimin¬ 
ished by hypertrophy of the chlorenchyma, reduction of air spaces, and 
number of stomata, by production of inhibitory excretions, by alteration 
of the osmotic relations of the infected cells and by injury to the water¬ 
absorbing parts. 
The final or aggregate effect of rust infection on the water requirement 
of cereals has not been adequately determined. Since Weaver’s results 
were secured with seedlings for a short growth period, it seemed that 
further work was necessary to obtain evidence in regard to the following 
three questions : 
Is the transpiration of rusted wheat plants sustainedly greater than 
that of healthy plants throughout the growth period? 
Is the amount of water transpired for the production of a unit weight 
of plant substance greater in rusted than in healthy plants, and are grain 
and straw production affected in the same way ? 
Is the effect on water requirement different in the case of infection by 
leaf rust and by stem rust, and is this effect related to differences in char¬ 
acter and sizes of pustules ? 
experimental methods 
Marquis wheat was selected for the experiment, together with several 
strains of stem rust which produce large confluent pustules and no 
chlorosis on this host, and a mixture of collections of leaf rust to which 
this variety was readily susceptible. The plants were grown in Wausau 
quartz sand of a grade having a moisture equivalent of 3 per cent and a 
maximum water capacity of about 12 per cent. Crocks of one-half gal¬ 
lon capacity, provided with a drain at the bottom, served as pots. Two 
thousand eight hundred gm. of air-dry soil were placed in each. Three 
hundred cc. of nutrient solution were added, thus bringing the water 
content close to the maximum capacity, and one plant was set in each 
crock. The soil moisture content was maintained by weighing the 
crocks first at weekly and then at three-day intervals, and water was 
added to restore the base weight. The crocks were sealed with wax 
so that water loss was restricted to the plant. Although in the latter 
part of the growth period transpiration became very great, owing to the 
high diurnal temperatures in the greenhouse, there was no indication of 
