NOSTOC. 547 



with interspaces tilled with Nostoc. If other algae, e.g. Oscillaria, 

 enter the cavities, the opening is neither closed nor do the walls 

 grow out as processes. Infection by Nostoc only occurs when 

 the mucilage-cavities lie near the apex of the thallus and are 

 secreting mucilage, the substance which evidently stimulates the 

 Nostoc to enter. 



Leitgeb found many Anthoceroteae {Dciulroccros, Nototylas, 

 Anthoceros) with mucilage-cavities containing Nostoc, not sunk 

 in the thallus as with Anthoceros laevis, but forming warty pro- 

 jections above it. In the case of Dendroccros these occurred on 

 the upper side of the thallus as well as on the lower. The 

 openings of the cavities of Nototliylas do not close after infection, 

 but distinctly open wider. 



Janczewski observed that chlorophyllous cells of Hepaticae, 

 though at first unintiuenced by the intruding alga, afterwards 

 lose their chlorophyll and plasma ; hence he assumed that the 

 imprisoned Nostoc begins in time to live a parasitic life, and to 

 kill the host-cells. This, however, is not supported by other 

 authorities. Goebel, on the other hand, believes that the Nostoc, 

 like the mucilage amongst which it grows, is useful to the 

 thallus, and that it ultimately completely replaces the mucilage. 

 I'rantl held that the alga assimilated free nitrogen, giving 

 up the product to the hairs in the cavity ; but this is ex- 

 tremely unlikely, especially when the Nostoc is cpmpletely enclosed 

 in its host. 



Nostoc lichenoides is also very frequent in the leaf-auricles on 

 the under side of the thallus of Blasia pusilla. The auricles 

 contain mucilage, which probably induces the Nostoc to enter. As 

 a result of the Nostoc iiivasion the auricle enlarges and continues 

 to live, whereas without this it would soon have died off. 

 Branched filamentous processes are produced from the inner wall 

 of the auricle and grow amongst the Nostoc} 



B. THE TRUE ALGAE. 

 In these Algae the green chlorophyll is limited to certain 

 portions of the plasma, the chromatophores. The true Algae 

 are capable of sexual reproduction. They are all more or less 

 adapted to an aquatic life. Many of them live in symbiosis, 

 some are true parasites. 



' Waldner, Akad. d. Wissensr/iaften in Wien, 1878. 



