BoT.-VoL. I.] PETRCE— NATURE OF LICHENS. 215 



tap-water. In this preparation the spores all died within 

 three days, the protoplasm disappeared, the oil drops 

 became confluent and filled the cell-cavities. Excess of 

 water, inadequate diffusion of oxygen and carbon-dioxide, 

 checked respiration, the diffusion into the water of some 

 poison contained in the vaseline used for sealing — all or 

 any of these may have been the cause of death and of the 

 breaking down of the cell-contents. Bacteria were practi- 

 cally absent. 



If it were possible to clean an apothecium so thoroughly 

 that no bacteria would be carried by the spores ejected 

 upon the cover-glass, it seems probable that agar-agar would 

 prove a good medium upon which to cultivate lichens from 

 the spores. This is conceivable but not readily attainable. 

 If practicable, agar-agar cover-glass cultures would be very 

 useful, for they could be minutely watched with the high 

 powers of the microscope. 



In the cultures just described, made during the latter part 

 of the rainy season, in February, only one cell in each 

 spore put out a germ-tube. Water cultures begun about 

 the middle of March, when it was warmer out of doors and 

 the rains were practically over, were more successful in 

 that both cells of some spores germinated, though in all of 

 these the tubes from the two cells were unequal in length, 

 and only one tube from a spore branched. 



Having obtained germinated spores by means of these 

 cultures, I attempted to reconstruct a Ramalina by putting 

 these where they could easily reach gonidia from a Rama- 

 lina thallus. The method employed was this: Into a tap- 

 water hanging-drop culture of R. reticulata fragments and 

 isolated gonidia, obtained in the way described on page 218, 

 I introduced by sterilized platinum loop a number of germ- 

 inated spores, stirring gently so as to mix the spores with 

 the gonidia. Germinated spores were thus brought close 

 to isolated and apparently healthy gonidia. One would 

 naturally expect the germ-tubes to be chemotropically 

 attracted by the gonidia and to bend towards them. As 

 illustrated by fig. 4, the hyphae put forth by the spores did 



