8 BOTANICAL GAZETTE. | March, 
to that of the other species of the group. It seems to have 
been more abundant during the last season than ever before, 
but we must remember that its host, Portulaca oleracea, isa 
low juicy plant, even when rowing upon the dry hot earth. 
The mildew was therefore supplied with plenty of moisture. — 
That it seemed to thrive better the past year than _ before 
may arise from a lack of vigor in the host, so that the same 
ora smaller actual amount of the parasite gave more evi- 
dences of destructive work during a dry season than on an 
average year. On sucha year as this there are greater facil- 
ities for the quick dispersion of the conidial spores. The 
host, being low, receives all the dews, and the dry, dust-like 
spores, which have been scattered during the day, germinate 
in the moisture of the night. Nevertheless, it is probably 
the disease retained their normal prostrate position. It was — 
spores. In walking over a piece of ground covered with 
purslane, the feet will hit the dusty, spore-laden, upright 
dee and send the conidia to some distance. The same 1s, 
of course, true when the feet of passing animals strike the — 
vertical branches. | : 
ae econ hea, the facts of observation show that the 
Species of Peronosporez are best suited to moist weather. No 
ing the ] genus Peronospora has been as abundant dur- 
Pith # ast two seasons of drought as before. There was a 
— e _ of mildew the past season over last year. 
Seneral, the mildews were found in early spring, while 
, all through the dry rainless 
summer, they occurred in limited quantities, and only upon 
; ,» along streams and the edges of 
pools.. A few. weeks after the refre P 
ing in shady places. The 
~ = 
» 4S a rule, there was less of any of the ‘ 
enced by drought, but 
species, and the infested specimens were those growing in 
