BOT.-VOL. I.] PEIRCE— NATURE OF LICHENS. 219 



The individual behavior of the isolated gonidia, fairly 

 scattered throughout the hanging drop, could be easily 

 followed. Many of them were entirely free from any trace 

 of hyphie, while some had short pieces of hyphae still 

 attached to them. Of the latter, some gonidia, as shown 

 by fig. 12, had haustoria in them, while others appeared to 

 have the hyphae only adhering or attached to the outside 

 (fig. 7). A difference in size and in subsequent behavior 

 between those gonidia absolutely free from the fungus, and 

 those upon which and in which fungus fragments still 

 remained, is to be noted. Those gonidia which, though 

 enclosed within the Hchen, have not been invested by 

 fungus hyphae, still less penetrated by haustoria, are larger, 

 deeper green, and in every way healthier looking than the 

 others. How is this to t>e accounted for ? 



The enclosed but not invested algal cells seem to me 

 to be the only ones in the Hchen thallus which are at 

 all advantageously situated. They do have a more con- 

 stant supply of aqueous solutions of food materials than 

 their fellows outside, they are shaded from excessive light, 

 screened from excessive heat, protected from excessive 

 dryness, shielded perhaps from -sudden changes of any 

 kind, possibly manured by the excreta of the fungus. In 

 these ways they may be better off than their unhoused 

 fellows, and sometimes at least they are larger. They 

 are not subject to the drain upon their vital energies 

 which those gonidia invested and penetrated by hyphae 

 must withstand if they are to survive. The fungus can 

 obtain from these gonidia with which it is not in permanent 

 and intimate contact only such substances as diffuse from 

 them into the water of the lichen-body; whereas it can 

 withdraw through a haustorium within the cell, and even 

 through the cell-wall with which a hypha is closely in 

 contact, the foods elaborated by the gonidia for their own 

 use. Gonidia not invested by hyphae are to be found in 

 every preparation. They are conspicuous from their larger 

 size, deeper color and generally healthier appearance. It 

 may have been these which suggested the notion that green 



