188 
president’s address. 
June, 1888. 
mouth closed with a plug of cotton wool; the whole is then 
sterilised by steaming. A small portion of the material to 
be observed is transferred by a platinum needle, previously 
heated in a flame, to the surface of the gelatine in the tube, 
which (since the material is solid) can be held upside down 
during the operation. The plug of wool is then restored, 
and the tube kept at the appropriate temperature in an 
incubator. If all the precautions are duly observed, the 
result will be a characteristic and easily watched growth in 
the gelatine at the bottom of the tube. 
Well boiled potatoes, cut in halves with a sterilised 
scalpel, also furnish a suitable medium for growing certain 
kinds, and, if they are kept under glass covers, accidental 
contamination may be avoided. The lianas, the glass covers, 
and everything else which comes near, but is not in actual 
contact with, the cultivated material, can be washed with 
corrosive sublimate solution to kill any germs that may be 
upon them. 
It is by the adoption of equally careful precautions 
that successful results have been attained in the cultivation 
of the Uredinese (Leaf-Fungi). In both cases it was seen long 
ago that nothing but such certainty of cultivation would ever 
enable us to come to correct conclusions upon the biology 
and the species limitation of these particular groups, but in 
both cases, when the desire first manifested itself, it seemed 
hopeless of realisation. The fact that such success has been 
reached in the propagation of Fungi in these two groups 
should confirm onr hopes that similar success awaits the 
ingenuity of some one in regard to other groups, where 
similar knowledge would be equally invaluable. It is some¬ 
what strange that the greatest certainty of “ pure ” cultiva¬ 
tions should have been attained in the treatment of the most 
minute Fungi, in which a priori one would have expected the 
greatest difficulty. 
One of the points of interest in connection with the 
Bacteria, which has aroused very considerable warmth of 
argument, is the question of their pleomorpliism, as it is 
termed, that is, their capacity for assuming at different 
stages of their growth different morphological characters, so 
different in fact that they would be set down, if independently 
observed, as distinct and even widely distinct species. 
It is obvious that the method of “pure” cultivations affords 
a means of settling this formerly vexed question in a satis¬ 
factory manner. Many such series of experiments have been 
performed, and the ultimate result has been to confirm the 
opinion I have always expressed, that this pleomorpliism is 
