2l6 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



not bend at all. The hypha figured was about half as 

 long when the germinated spores were sown in the 

 gonidia culture. It continued to grow straight on, did 

 not branch, and never united with the adjacent or 

 with any other gonidium. The same is true of all the 

 others, and although I kept the preparations until all the 

 gonidia were evidently dead, though the hyphas still looked 

 healthy, no union of hyphge and gonidia took place. 

 Undoubtedly the bacteria, which overran these cultures 

 within a week after they were made, are responsible for 

 the failure of the gonidia to attract the hyphee, of the hyphae 

 chemotropically to respond, and of the two to form a new 

 lichen. That the failure of the attempts just described is 

 not due to an unhealthy condition of the gonidia produced 

 by the isolation is proved on page 220. 



DeBary (1887) reports from Stahl's (1877) investiga- 

 tions on the formation of the lichen-thallus, that "smaller 

 branchlets are formed at the points of contact" of the 

 hyphae with an algal cell, which closely embrace it and 

 enclose it in fresh ramifications. Whether actual contact is 

 necessary, whether the gonidia stimulate the germ-tubes to 

 bend or to branch, whether the union of gonidium and 

 hypha is always by branches of the germ-tube and not by 

 the tube itself — these are questions which renewed investi- 

 gations onl}'^ can answer. When, by greater skill and better 

 methods than I have possessed, one is able to put together 

 isolated healthy gonidia and healthy germinated spores, in 

 hanging-drop cultures free from bacteria, the formation and 

 growth of the lichen can be followed, step by step, from 

 the chemotropic behavior of the germ-tubes to the complete 

 investment of the gonidia by the fungus. 



III. The Relations of Gonidia and Hyph^ as 

 SHOWN BY Cultures. 



Although I have been unable to reconstruct a lichen, 

 still I believe that by other means I have obtained some 



