16
Scientific Memoirs by
the season itself was unusually backward, so that a fresh spring vegetation had
not yet sprung up to hide these spore-laden dry grass leaves. I placed some of
these teleutospores on a few young leaves of one branch of a Strobilanthes
plant I had gathered during the previous autumn, and which I had since kept
in my verandah. In nature these plants were still without leaves thus early in
spring, and but for the forced plants I had in my possession, collected and
housed during the previous year, I should have had no opportunity then of
ascertaining whether these teleutospores were related to the æcidium in ques-
tion. Most of these leaves became infected, and as soon as this indication was
afforded of the further life history of the Strobilanthes æcidium, numerous other
experiments were instituted, many of which are detailed below, and which I
think prove beyond doubt the genetic relationship between the puccinia-bearing
fungus on Pollinia and the æcidial parasite on S t r o b i l a n t h e s .
The method of inoculation* I pursued was usually as follows, and, unless
otherwise stated, all the following experiments were made in this way. Into a
few drops of distilled water held in a watch-glass, a large number of teleutospores
scraped off their beds were placed. This water was then applied by a clean
glass-rod or other instrument to the leaves or other parts which it was desired to
infect.
But before proceeding to a description of these experiments, it is desirable
to note the general characters of the æcidium as it occurs on Strobilanthes.
The affection is especially prevalent on young plants some time before
flowering. The leaves present from one to a dozen or more circular discoloured
patches on their blades, measuring on an average 4—5 m.m. in diameter, though
some were 13—14 m.m.; and these are usully bulged downwards with a concavity
above (fig. I). These patches, as seen on the upper surface of the leaf, are yel-
lowish green ; but as they increase in size, their centres become more purely yellow,
whilst the margins only remain greenish yellow. On the upper surfaces a few
minute points may be seen which are spermogonia. The lower surfaces of these
patches, when young, are rosy, flesh-coloured or pale purplish, becoming yellow
when the æcidia are ripe. The affection is mostly confined to the lamina of the
leaf, and but rarely occurs on the petiole in nature, though, in artificial inocula-
tions, I succeeded in infecting the petioles and even the stem on several occa-
sions (fig. 8).
Experiment I.—This experiment has just been alluded to. The branch
referred to as having been first inoculated had eleven new leaves, and spores
were placed upon each of these on 1st April. On the 19th two leaves appeared
to have become infected, for they presented paled spots, although as yet there
were no indications of any fructification. Up to this date the plant, which was
* I shall frequently make use of this word in the following pages, meaning simply the application of
spores to the surfaces of the plants, although I am aware that it is strictly incorrect to employ it in this sense;
but as its use will save frequent paraphrasis, I hope it may be excused, just as with much greater indul-
gence the word vaccination is permitted to include operations not covered by the literal meaning of the
word.