the Change of the Gonidia of Lichens into Zoospores. 105 



escape ; and under the action of iodine the membrane of these 

 cells was coloured violet, whilst the extremity of the filament 

 to which they were attached was of a pale yellow. 



3. We 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 crowing on it was fixed on the exterior of a larce 

 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 appeared. 



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 protuberance 

 at the commencement of the division, the others preserving to 

 the end their regular spherical form. 



We also submitted these two lichens to similar experiments, 

 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 de- 

 cayed 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 : — 



1. Not only Algai and Fungi, but Lichens also, are provided 

 with zoospores. 



