185 
these cells was coloured violet, whilst the extremity of the 
filament to which they were attached was of a pale yellow. 
“ 3. W e have equally obtained zoospores from gonidia 
united into a considerable mass. Some, indeed, of these 
cellules were already empty, the zoospores having escaped, 
whilst, on the other hand, others had undergone no change. 
“ 4. Lastly, we have found, on the bark of a birch tree in 
the garden of the University (of St. Petersburg), green 
patches exclusively formed of free gonidia, completely 
destitute of thallus. These cellules also produced zoospores 
perfectly identical with those of the gonidia which we had 
sown. 
“ The formation of zoospores by sowings requires always 
many weeks, as the following experiments demonstrate : 
“ First experiment . — Vertical sections of a thallus of 
Physcia were placed, March 13, on fir-bark. The issue of 
zoospores was first observed April 19. 
“ Second experiment . — On March 21 a bit of lime-bark with 
a lichen growing on it was fixed on the exterior of a large 
glass vessel filled with water, which was made to fall on it 
drop by drop by means of a cotton wick curved siphon-like. 
On April 1 the filaments of the lichens were disintegrated. 
On April 3 we transferred the gonidia, as well as the mucous 
mass of decomposed filaments, to two bits of bark. On April 
20 the zoospores appealed. 
“ Third experiment . — The lichen was immersed until the 
complete disintegration of the filaments, and on April 3 the 
gonidia were placed on gravel, on the earth, and on bits of 
rotten wood. Those on the two former became decomposed 
by too much moisture; but those on the latter succeeded 
well, and on May 15 the zoospores were observed. 
“ The gonidia which did not produce zoospores separated 
into a great number of motionless spherical cellules, amongst 
which we distinguished two forms — one presenting a protu- 
berance at the commencement of the division, the others 
preserving to the end their regular spherical form. 
“ We also submitted these tw T o lichens to similar experi- 
ments, except that, instead of vertical sections of the thallus 
or of gonidia already isolated, we used the soredia from the 
surface of the thallus, and sowed them either on bark or bits 
of decayed wood. Their gonidia presented precisely similar 
results to those of the Physcia, both in their form and their 
ulterior development. 
“ These observations authorize us to propound the following 
propositions : 
