Scientific Memoirs by
four pores very clearly. Some spores from Prenanthes were placed in water on
the 14th April, and next day they had germinated freely (fig. 6), throwing out
long germ tubes, mostly branched and very long. The spores from Lactuca
also germinated freely and in the same way the germ tubes containing orange red
matter. The spermogonia are numerous, with tufts of paraphyses protruding
through their mouths.
I uprooted some of these attacked plants of Prenanthes found in nature
with æcidia and kept them in a gardener's box with their roots in a glass vessel
of water. At the end of April I found that some new leaves, which had been
put forth bore brown pustules, mostly hypophyllous, on large areas of mycelial
invasion, which retained their green colour for some time after the rest of the
leaf blade yellowed from withering or decay. These pustules bore uredospores.
Each leaf bore two to twelve pustules; but in nature the whole leaf surface is often
besprinkled with them. The uredospores are pale brown, very deciduous with-
out any portion of stalk adhering, round oval or pyriform, covered sparsely with
minute spines, and measuring when fresh 26-21 X 21-18 μ . Those from Lactuca
measured 26-19 x 23-17 μ . There are pale semi-lunar thickenings on the epi
-spore, one to three being visible at once, implying from four to five on each
spore (figs. 2, 5, 6). These semi-lunar excrescences swell up in sulphuric acid
and gradually disappear. I frequently placed these spores from Prenanthes in
water, but they persistently refused to germinate. Spores from Lactuca germ-
inated tardily, emitting a straight, unbranched tube, containing very pale orange-
red matter, and leaving the spore-walls grey.
After producing these uredospore pustules, my Prenanthes plants unfortu-
nately died—at least the parts which bore the parasite. On the i st November, how-
ever, I found some plants in nature, not far from the locality where I had found
the aecidial stage, bearing teleutospore pustules. The leaves were well sprinkled
on their lower surfaces with irregularly disposed minute black pustules, the upper
surfaces opposite them being spotted with yellow dots. Immense numbers were
found on a single leaf. The spores, which were typical Puccinia spores, are
rounded at both ends, plump, very deciduous, falling off with only a fragment
of stalk adhering or none at all (fig. 3). They are brown, tuberculated over both
cells, not thickened anywhere, and with a nuclear vesicle in each. The fresh spores
from Prenanthes measure 26 or 3o p in total length by 22 to 20 p at the septum,
where the spore is very slightly constricted. The spores from Lactuca, on the
other hand, measured 34-26 x 23-18p (fig. 7). There is no apical thickening.
At this time the plants bore no uredospores. These teleutospores would not ger-
minate at once ; they evidently required to pass through a period of quiescence
I preserved some of these spores from Prenanthes until the following spring, but
from some cause they had lost vitality, and I was therefore unsuccessful in all my
attempts to reproduce the æcidial stage. The history above sketched leaves
no doubt, however, that the fungus is a complete autcecious species.
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