SPECIAL ADAPTATIONS 37 r 



Chlorophylloiis animals. In lichens, as in grafts, the component parts 

 are simply in close contact but remain distinct, whereas many tiny algae 

 actually live, grow, and divide within the cells of certain animals, chiefly 

 Protozoa, but including also Metazoa (Hydra viridis, Convoluta, &c.). It 

 is not, however, certain in all cases whether we are dealing with chloro- 

 plastids or with symbiotic algae, for in certain protozoa ( Vorticella cam- 

 panula) diffuse chlorophyll may be present, and hence it is easy to 

 understand that definite chloroplastids may have been differentiated in 

 higher forms 1 . 



Leguminosae afford instructive examples of reciprocal symbiosis, 

 for in the cells of the non-chlorophyllous root-nodules of these plants 

 a bacterium develops, by means of which free nitrogen can be assimilated 

 (Sect. 69). 



Mycorhizas, or associations of fungal mycelia with roots, occur in 

 almost all phanerogamic saprophytes, and also 

 in many plants which possess an abundance 

 of chlorophyll 2 . Endophytic mycorhizas, in 

 which the fungal hyphae penetrate living cells 3 , 

 are found in many of the Orchidaceae, Erica- 

 ceae, and Epacrideae, whereas the epiphytic 

 mycorhizas of Monotropa, certain Cupuliferae, 

 &c., simply form an external covering to the 

 roots. In trees the presence of a mycorhiza 

 usually induces a marked branching of the root 

 system, and since the mycelial hyphae often 

 spread to a considerable distance, they may be 

 of the utmost importance in enabling sapro- 

 phytes to obtain organic nutriment from humus, 

 especially since in such plants root-hairs are often feebly developed or 



1 Biitschli, Protozoen, 1887-9, Bd. HI, p. 1473; Dantec, Ann. d. 1'Inst. Pasteur, 1892, T. VI, 

 p. 190, and the literature there given. Cf. also Sect. 52. Algae often occur merely as epiphytes 

 in the intercellular spaces, or mucilage cavities of certain plants. On the occurrence of Nostoc in 

 Gunnera, see Jb'nsson, Bot. Centralbl., 1894, Bd. LIX, p. 12. Also Mobius, Biol. Centralbl., 1891, 

 Bd. xi, p. 545 ; Schneider, Bot. Centralbl., 1894, Bd. LIX, p. 13. 



3 Frank, Ber. d. Bot. Ges., 1885, p. 128, and xxvn, ibid., 1887, p. 395 ; 1888, p. 248 ; 1891, 

 p. 248 ; P. E. Muller, Bot. Centralbl., 1886, Bd. xxvi, p. 22 ; Johow, Jahrb. f. wiss. Bot., 1889, 

 Bd. XX, p. 475 (Saprophytes) ; Schlicht, Landw. Jahrb., 1889, Bd. XVIII, p. 499 ; Hb'veler, Jahrb. f. 

 wiss. Bot., 1892, Bd. XXIV, p. 302 ; Sarauw, Beibl. z. Bot. Centralbl., 1896, Bd. VI, p. 24; Groom, 

 Annals of Botany, 1895, Vol. IX, p. 356; Janse, Ann. d. Jard. bot. d. Buitenzorg, 1896, T. XIV, 

 p. 180. The other literature is quoted in these works, and in Frank's Lehrb., Bd. I, p. 274, and 

 Krankheiten d. Pflanzen, 1895, 2. Aufl., Bd. I, p. 293. 



8 Neither the injection of living organisms nor the penetration of certain parasites (cf. de Bary, 

 Pilze, 1884, p. 422) necessarily leads to the death of the protoplast, as is shown by the symbiotic 

 union of algae and certain infusoria, by the fact that the nitrogen-assimilating bacteria may remain 

 living in the cells of root-nodules, and also by the fact that certain rotifers may inhabit Vaucheria 

 filaments. 



B b 2 



FIG. 54- Section of root of Calluna 

 vulgaris showing endophytic myco- 

 rhiza (X 375). 



