of Edinburgh. Session 1874-75. 501 
in devising and skill in carrying out delicate mechanical con- 
trivances, and of the eloquent as well as cogent logic with which 
he enforced his conclusions. I wish it had fallen to one more fit 
to do justice to the subject, to lay before the Society an abstract or 
summary of this very remarkable paper. 
Professor Lister’s work may he considered from several different 
points of view. 
I. As a contribution to microscopic botany, and as such it takes 
a very high place. A great obstacle in the way of the study 
of microscopic plants is the difficulty of the determination of species. 
Each species is liable to great variation in form, and there is a great 
general resemblance between forms assumed by different species. 
To get over this difficulty, the method of “ cultivation” has been 
made use of — the doubtful specimen is kept and grown to see what 
it will become. Professor Lister in this paper describes his novel 
method of cultivation, in which the fungi are made to grow in 
various kinds of soil. Thus, two fungi growing in Pasteur’s solution 
may resemble one another very closely; but if transplanted into 
milk, and allowed to grow there, a very marked difference may be 
produced. Or two fungi may present in one solution forms indis- 
tinguishable from one another, but one may grow luxuriantly and 
the other not at all, when transferred to a different solution. Such 
cultivation experiments are apt to fail from a character which they 
have in common with cultivation experiments on a larger scale. 
The miniature garden, like other gardens, is liable to be infected 
with weeds, and it sometimes happens that such a weed, or unwel- 
come intruder, is mistaken for the produce of the seed sown or the 
plant planted. These weeds grow either from seeds contained in 
the soil, or introduced from without, and it is essential to a success- 
ful experiment that the first be killed or removed, and the second 
excluded. Professor Lister secures the necessary condition of 
purity of the soil, perfect freedom of his solutions from all trace 
of life except those fungi or germs purposely introduced, and per- 
fect security against accidental or unintentional entrance of any 
living thing, without interfering with the readiness of access to 
each experiment during its progress. This is accomplished by 
means of devices, of which it is difficult to say whether the com- 
plete success or the wonderful simplicity is more striking. Th% 
