ii8 CJiapters in Modern Botany chap. 



a higher and more complex one ; and it is a microcosm of 

 nature to boot. 



It is also interesting to notice the existence of what 

 Zukal calls "half-lichens," in which the mutual partnership 

 has not been thoroughly established. For certain fungi 

 usually occurring as lichens may, in certain conditions, live 

 bereft of their partner-algae, as saprophytes ; while others, 

 which are usually parasites or saprophytes, are sometimes 

 found combined with algae, and forming lichens. We have 

 thus what we may fairly consider lichens in the making. 



An interesting parallel to the case of Hchens, in which 

 the part of the fungus may be taken by animals of very 

 various kinds, is that of the " yellow cells," first known 

 as practically constant features of the organisation of the 

 Radiolarians, and long supposed to form an essential part 

 of these, but also occurring in the tissues of many much 

 higher organisms, especially Coelenterates. Notably the 

 large sea-anemone Aiithea cereiis^ which prospers and multi- 

 plies greatly in consequence. These yellow cells survive 

 after their host dies, or even after being isolated ; they 

 divide like unicellular algae ; they contain starch, and a 

 pigment like that of Diatoms ; they have a wall of cellu- 

 lose, and they evolve oxygen during sunshine. There- 

 fore they are regarded with justice as partner alg^. As 

 they live they remove carbonic acid and nitrogenous waste 

 from their partners, and evolve oxygen which acceler- 

 ates the vital processes of the animal ; they form starch, 

 which when dissolved passes out by exosmosis into the 

 animal tissues ; when they die they are digested. The 

 partnership is therefore one of benefit to both parties. 

 There has been considerable dispute as to details, but the 

 general facts of this symbiosis between plants and animals 

 are admitted by all. 



Strasburger has discovered an interesting association 



