The white Uredo can scarcely have escaped the observation
of any one interested in the vegetable productions of nature.
Oil the Shepherd’s Purse, so common by road-sides, it
is to be found throughout the greater part of the spring and
summer, variegating the leaves with its white spots, and often
distorting the flowering-stems. In gardens it is more conspicuous,
for it often attacks the cabbage and the cauliflower, or
other varieties of Brassica olerácea, forming large blotches on
the leaves, each composed of many irregular spreading spots or
clusters of sporidia, whose white colour forms a strong contrast
to the dark green hue of the plant.
On the Shepherd’s Purse, the Uredo candida forms a nidus
for another parasite, the Botrytis parasitica of P e r s o o n ,
—a little plant which has been confounded by some writers
with the uredo itself, hut to which it bears no resemblance.
It is rather doubtful whether there be more than one species
of white Uredo. D e C a n d o l l e thought differently at
one period, but seems to have satisfied himself that one only is
known, in the supplementary volume to the Flore Française.
The Uredo Cheiranthi of P e r s o o n , is, however, said by M.
S c h w e i n i t z to be really distinct. I t is a species I have not
seen.
Fig. 1. U. Candida, on Thlaspi Bursa-pasioris. Fig. 2. The same on a portion
o f a Cabbage leaf, natural size. Figs. S. & 4. Plants o f the same.
F ig. 5. Sporidia; magnified.