40 BOTANICAL GAZETTE [JULY 
of these dews seem to form just before sunrise in California, so that 
they exist only a short time. On misty nights, with heavy dew, a 
most vigorous germination takes place, easily sufficient to produce 
infection. It has even seemed to the writer that germination in this 
way is more vigorous than in drops of distilled or tap water placed 
on the slide, though no exact comparisons have been made. 
Something remains to be said as to the influence of soil moisture 
upon the rust in California. In the island district the wind effects 
are so absolute that all other features are of secondary importance. 
Soil moisture increases the amount of dew, and since almost all this 
country has abundant natural subirrigation, it is desirable to keep 
the surface as dry as possible. In the case of one plantation, particu- 
larly, situated in the strongest wind belt and where the nights were 
particularly dry, no rust whatever has developed, though in a center 
of infection, although the soil became so dry through neglect that 
cracks opened six inches wide and four feet in depth, and the aspara- 
gus roots were almost killed. It should be fully understood, how- 
ever, that in this case there was absolutely no moisture in the air to 
germinate spores. A sheet of tissue paper lying on the ground would 
be as dry and crisp at sunrise as at noon. Such conditions are never 
approximated in the east. 
At Milpitas, with considerable dew on all the beds, differences 
in soil moisture are more apparent. Some of the beds here are 
left unirrigated and uncultivated in summer and become extremely 
dry. In these the rust makes much more rapid headway than in the 
irrigated beds, and the tops are killed to the ground, while the others 
still have the green bottom (jigs. 17, 18) late in the season. It is a 
general principle, in fact, that in this district, where conditions 
resemble those of the east, except for the absence of summer rain, 
the driest beds rust first and most completely, while those kept wet 
throughout the summer are the latest and least affected. This 
could not be shown more plainly than by the field in which fig. 20 
was taken. In this case a stream of water was being run past the 
end of a very dry asparagus field for irrigating lower down. When 
the whole field back to the right was dead with rust, the end plants 
in each row, next the water, were green and vigorous, as shown in 
the illustration. It is difficult to imagine how more absolute proof 
