134 W. ARCHER. 



impossible. Thick sections from this substratum are much 

 too indistinct, and very thin ones do not admit of tlie course 

 of the hyphae being followed. Now, so long as this con- 

 nexion is not clear, no conclusion can be drawn from the 

 occurrence of young Xanthoria thalli in the place where 

 spores and algae were sown, since soredia indeed might give 

 rise to the same phenomenon. However, I may here add 

 that the commencing lichen formations almost always 

 were without the aspect of having owed their origin to 

 soredia. 



Culture experiments on the minnte scale (''Kultuurproeven in 

 het Idein "). — The spores were brought upon slides and kept in 

 moist air. In the beginning of my experiments I occasionally 

 placed the slides under the microscope for the purpose of 

 examining the advance made in germination by the spores 

 and the growth of the algae ; afterwards, however, I left the 

 slides uninterruptedly in the moist medium, in order to follow 

 out the results microscopically in the conclusion of the 

 culture. The last is much preferable, since the frequent 

 transporting of the slides whereon the cultures take place 

 adds to the opportunities for the dire enemy of these experi- 

 ments — mould — to reach the slides. 



In a part of my cultures of last year along with the 

 spores and algae, a little solution of the ash of those lichens 

 whence the spores proceeded was sprinkled upon the slides 

 by means of a little brush ; in this way the moisture falls on 

 the substratum only in little drops ; this was done in order 

 to supply the inorganic nutriment which, according to Reess, 

 the lichens derive during their development from the sub- 

 stratum. That this did not take place in all cases was owing: — 

 (1) to the fact that, however carefully I -went to work, large 

 drops occasionally formed upon the substratum, which not only- 

 hindered the germination of the spores, but also favoured the 

 formation of mould ; (2) that the application for the purpose 

 of my cultures on the minute scale (" in het klein") was not 

 directly necessary ; the germinating filaments of a parasitic 

 fungus must still be forced into or against the host (the first 

 in endo-, the second in epiphytes), before all the protoplasm 

 is used up from the sjiore, because otherwise the necessary 

 organic nutriment is absent to enable it to execute this move- 

 ment of growth. 



It is probable, indeed, that on the germinating filament 

 of lichen- spores reaching the Cystococcus-ceWs the spores often 

 contain sufficient reserve material to enable the germ-tubes 

 to continue growing for some time. It would further be 

 very probable that, even after the whole of the reserve nutri- 



