LICHENES. 30? 



slaves not at all related to the hyphae ; in the other they are produced 

 by them, and after a brief period of freedom are fastened upon, and 

 compelled to do service for the hyphae which produced them. 



It is impossible to decide between these two theories until further in- 

 vestigations shall determine the truth or falsity of Dr. Minks' state. 

 meut as to the origin of microgonidia. It must, however, be said, that 

 the view which appears to be most in accord with what we now know 

 of plants, is that taken by Schweudener. 



(b) 1. Cultures of lichens have been made by many observers, 

 especially by Hornet, Reess, and Treub. The latter made an extended 

 series, from which the following details of methods are condensed. 

 Spores may be secured for germination by placing freshly gathered 

 lichens upon plates covered with well-moistened glass slips, and keep, 

 ing them under a bell-jar for from twelve to twenty-four hours, at the 

 end of which time a number of spores will be found on the slides. 



2. The spores may be left upon the slides and allowed to remain in a 

 moist atmosphere, as in a bell-jar. Others may be placed upon very 

 thin pieces of the bark upon which the lichens naturally grow. Still 

 others may be made to grow in the presence of a small quantity of the 

 ash of the same species of lichen. 



3. A too copious supply of moisture is unfavorable to the successful 

 germination of the spores. If the conditions are favorable germination 

 will begin in from two to eight days. In about a month after sow- 

 ing, the protoplasm of the spore becomes in great part used up in the 

 formation and elongation of the germinating filaments. It always hap- 

 pens that the growth of the hyphse from the spores ceases soon after the 

 exhaustion of the protoplasm, unless the hyphse come in contact with 

 algae of the proper kind, or with gonidia. 



4. An interesting culture may be made by repeating Bornet's exper- 

 iment, as follows: He placed on fragments of bark, previously boiled 

 to kill all other germs, and also on pieces of limestone freshly broken, 

 a layer of Protococcus viridis scraped off of a damp wall, and to this 

 added the spores of Thelosclds'es parielinus. In about a fortnight the 

 hyphse were seen to be large and ramified ; wherever they came in 

 contact with cells of the Protococcus they adhered either directly or by 

 means of lateral branches. Bornet made at the same time parallel cul- 

 tures, without, however, bringing the germinating spores into proximity 

 to Protococcus; the growth was much less, and in no case did he get 

 any evidence that the hyphse themselves formed gonidia. 



5. Treub modified Bornet's culture by using, in some of his experi- 

 ments, the artificially isolated gonidia of one species of lichen for ex- 

 ample, of some species of Ramalina and the spores of a different one, as 

 Tlieloschistes parietinus. He also us^d glass slides for his cultures, 

 whether with gonidia or free algae, taking the precaution, however, to 

 allow the drop of water in which the spores and gonidia were placed 



