ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 219 



crnstaceous Lecanoreae, Lecideas, and Graphidaceas. The last group is- 

 not yet touched ou. With each family he gives a figure of the out- 

 standing characters of the genera, and a bibliography of important works 

 bearing on the special group. Diagnoses are written in Latin. A 

 synoptic key to the species is given at the head of each genus. 



Primitive Lichen.* — Elizabeth Acton has examined Botrydina vul- 

 garis, and finds that it is not, as is sometimes supposed, a green alga, 

 but is a composite plant consisting of a central group of algal cells im- 

 bedded in mucilage, which is traversed by fungal hyphas, both plants 

 growing symbiotically together. The fungal hyphaa formed an envelope 

 of considerable thickness. She concludes that it should be regarded as 

 a lichen, possibly one of the most primitive of existing lichens. Alga 

 and fungus are able to live separately. B. vulgaris occurs in damp 

 situations among mosses on rocks or on the ground. 



Useful Plants among Lichens. — V. Schiffner divides such plants 

 into three categories. 



1. Edible lichens for men or animals. — The gastronomic quality de- 

 depends on their content of lichenin and isolichenin (lichen-starch). 

 Lichenin is always associated with a bitter principle, but it can be re- 

 moved by frequent washing, and the plants made serviceable to man. 

 Such lichens are Cetraria islandica, Gladonia rangiferina, Evernise, Sticta 

 pulmonacea, Gyrophora proboscidea, G. cylindrica, G. esculenta, A lector ia 

 sulcata, and Lecanora esculenta. 



2. Lichens as medicine. — Cetraria islandica is the only one of service. 

 Chlorea vulpina is used by peasants in Norway to poison foxes, and Alpine 

 dwellers employ Thamnolia vermicularis in lung disease of pigs. 



3. Lichens in the Arts. — The following dyes are obtained : orchil, 

 cudbear, orchil-extract, French purple, and litmus. These are extracted 

 from Roccellse, Dendrographa leucophsea, Pertusaria dealbata var. violaria, 

 Lecanora tartarea, and Umbilicariafrustulata. Sticta pulmonaria is a sub- 

 stitute for hops in the brewing of beer ; Physica ciliaris and Evernia 

 prunastri are used in perfumery ; Cetraria islandica and Gladonia rangi- 

 ferina are occasionally used in the preparation of alcohol. 



Absorption of Water by Lichens. J — F. Sievers confirms ZukaFs 

 observations on this subject, viz. that crustaceous lichens absorb water 

 from the upper surface only ; foliose lichens on both surfaces. Among 

 crustaceous lichens there are modifications of this rule ; in some species 

 there are no cracks on the surface, and in that case the water penetrates 

 by injured places, or in others at the edge of the thallus. Parmelise, 

 with black, impenetrable under surface, absorb water from above ; 

 where rhizinae are well developed, they serve to hold water. In 

 shrubby lichens the hygroscopic nature of the thallus provides for 

 absorption from the moisture of the atmosphere ; thus Gladonia rctipora 



* Ann. Bot., xxiii. (1909) pp. 578-85 (1 pi.). 



f Naturw. Wochenschr. , xxiv. (1909) pp. 65-72 (25 figs.). See also Bot. Cen- 

 tralbl., cxiii. (1910) p. 22. 



I Wiss. Beil. 38 Jahresber. Ber. Landw. Schule Marienberg, Ostern. (Helm- 

 stadt, 1908). See also Hedwigia, Beibl,, xlix. (1910) p. 108. 



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