Symbiosis 
BY 
H. MARSHALL WARD, D.Sc., F.R.S., 
Professor of Botany in the University of Cambridge. 
Synopsis 2 . 
O RIGIN of the idea and of the term. Differences between 
parasitisim and symbiosis ( 1 ). 
Lichens, previously regarded as autonomous plants, are 
shown to be dual organisms, a symbiosis of Alga and 
Fungus (2). Controversy regarding the Lichen theory, and 
establishment of the latter by means of synthetic cultures (3). 
Other cases of symbiosis known previous to 1880 . Algae 
in the stems of Gunner a , and the roots of Cycas, in the thallus 
or fronds of Anthoceros and Blasia , Azolla , Lemna , & c. (4). 
Extension of the idea of symbiosis : insect-fertilization, 
epiphytes, &c. (5). 
Galls not necessarily due to insects, but may be due to the 
irritating action of Fungi or Bacteria. Phytocecidia of the 
Aleppo pine, &c. ( 6 ). 
Symbiosis in animals. Green Infusoria, Hydra , sponges, 
&c. (7). 
Mycorhiza, the roots of many humus plants curiously 
1 Paper read before a joint meeting of the Chemical and Botanical Sections of 
the British Association at Dover, 1899. 
2 The figures in parentheses refer to the bibliography collected at the end. 
[Annals of Botany, Vol. XIII. No. LII. December, 1899 ] 
O O 2 
