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CALIFORNIA ACADEMY OF SCIENCES. [Pkoc. 3D Ser. 



of the gonidia of this lichen, much less to kill them; and 

 hence the hyphte, well supplied with food, may also, at 

 least frequently, be active in growth and in other ways. 

 For twelve months in the year these lichens can, and 

 undoubtedly do grow, though the most rapid growth and 

 the most growth must be during the warmer later part of 

 the rainy season. 



If this is the case with the lichen as a whole, what is the 

 condition of those free algal cells entirely away from and 

 uninvested by fungus hyphte ? Throughout a normal dry 

 season on the west side of the Bay of San Francisco, the 

 fogs at night and the dews are sufficiently frequent and 

 heavy to wet fences, tree-trunks, branches, etc., etc. 

 Though this moisture evaporates quickly after the sun 

 appears, I doubt very much that Cyslococctcs-\{k(t algae are 

 so completely dried by day that they do not revive at night. 

 Indeed, spherical unicellular algse, Cystococcus, Protococctts, 

 etc., although less abundant here on tree-trunks, fences, 

 etc., than in many other parts of the world, can be found 

 alive at all seasons. On almost every fence old enough, 

 one may find the algas alone, or with a few hyphas among 

 them, or with more but still not enough to cover and shield 

 them from dryness, and so on up to mature and fruiting 

 Hchens of various species. In this region, at least, the 

 survival of algse like those in lichens is not dependent upon 

 their being protected by fungus hyphas against extreme 

 dryness. 



It is argued that because Hchens are found flourishing 

 where algae alone could not possibly survive — for instance, 

 on dry and sun-baked rocks — that this is evidence that the 

 association of alga and fungus is mutually beneficial. Con- 

 cerning this, R. reticulata offers a case in point. The algae 

 forming the gonidia of this pendant lichen could not possibly 

 remain alive in the air even if they could float in it. Yet, 

 is it any advantage to the gonidial cells of this lichen that 

 they are living, growing, multiplying, where the force of 

 gravitation and the insufficiency of food would forbid algae 

 free from fungus associates to survive ? The answer to 



