CHAPTER VII. — PHENOMENA OF VEGETATION. — LICHENS. 



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hand the same species of Alga may serve as host to different species of Fungi, and 

 serve accordingly as a component part in very different forms of thallus. 



The following list contains the genera and groups of Algae which are known 

 to form Lichens ; the reader is at the same time referred to Schwendener's and 

 Bornet's special works and to some others also which will be named below, and to 

 the general works on the Algae 1 . Figures 167-169 represent some of these Algae 

 as they appear in the thallus of the Lichen and in most cases in connection with the 

 hyphae of the Fungus by which they have been attacked. 



FIG. 167. Lichen-forming Algae. The Alga is in all cases indicated by the letter g, the assailing hyphae by //. A Protococcus 

 •viridis, Ag. (Cystococcus, Nag.) attacked by the germ-tube from a spore of Physcia parutina. B Scytoiiema from the thallus of 

 Stereocaulon ramulosum. C Nostoc from the thallus of Physma chalazanum, Mass. D Gloeocapsa from the thallus of 

 Synalissa Symphorea, Myl. E Protococcus sp. (Cystococcus) from the thallus of Cladonia furcatx, P. ACDE magn. 950, 

 B 650 times. After Bornet. 



i. Chlorophyll-green Algae. 



(a) With short usually round cells living free or loosely united, but not forming 

 filaments or cell-surfaces, the group of ' Palmellaceae ' : Protococcus, Kg., Pleu.ro- 

 coccus, Menegh., Cystococcus, Nag. (Figs. 167 A,E, 168), Dactylococcus, Nag., 

 Stichococcus, Nag. 



(b) With cells firmly connected together into filaments and cell-surfaces, the 

 group of ' Confervae ' : possibly species of Ulothrix and especially the Chroolepus- 

 forms (Trentepohlia, Mart., Bornet) (Fig. 169) distinguished by the orange colour 

 of the contents (haematochrome) in addition to the chlorophyll. To these may 

 be added the genus Phyllactidium said by Bornet to be the Alga of Opegrapha 



See especially Nageli, Cattnngen einzelliger Algen ; also Kirchner, Algenflora von Sehlesien. 



