234 BOTANY PAKT i 



Many Fungi and Bacteria are practically omnivorous, while others are extremely 

 exclusive in their selection of a substratum. Thus from ordinary tartaric acid 

 Penicillium only utilises the dextro-rotatory form, and Bacillus subtilis only llie 

 laevo-rotatory form. Aspergillus growing in a mixture of glucose and glycerine 

 utilises the former first ("election " of nutritive materials). If the glycerine alone 

 is given it is completely utilised. 



As is evident from their thriving upon such various substrata, Fungi have the 

 power of producing from the different carbon compounds (and also from nitrogenous 

 mineral compounds, such as ammonium tartrate, or even ammonium carbonate) 

 protoplasm, cell wall, nuclein, fat, glycogen, etc. 



While many Fungi inflict far greater injury upon their host plants 

 .by the decomposition they induce than by the withdrawal of the 

 nutritive substances, others produce a different effect. The Rust-fungi, 

 and the Agaricinae which attack trees, for instance, do comparatively 

 little injury to their host ; while the relation between host and fungus 

 in the case of the Lichens has been shown to be absolutely beneficial. 

 The Lichens were formerly considered to be a third group of the 

 lower Cryptogams and of equal value with the Algae and Fungi. 

 It is only comparatively recently that the discovery was made by DE 

 BARY and verified by the investigations particularly of SCHWEXDENER 

 and STAHL, that the body of the Lichens is not a single organism, 

 but in reality consists of Algae (e.g. Cyanophyceae), which also exist 

 in a free state, and of Fungi, which for the most part belong to the 

 Ascomycetes ; these Fungi only exceptionally exist apart from the 

 Lichen. The fungal hyphre within the Lichen weave themselves 

 around the Algcxe ; and while the latter occupy the upper or outer 

 side of the leaf-like or cylindrical thallus as the more favourable 

 position for assimilation, the hyphae come into the closest contact with 

 them and absorb from them part of their assimilated products. The 

 fungi in return provide the Algae with water, which, owing to the 

 acids excreted, is often rich in nutrient salts, and enable them to live 

 in situations in which they could not otherwise exist. The researches 

 of ARTARIS make it probable that peptone is also provided by the 

 fungus. As a result of this close union with the fungi, the Algae 

 are in no way exhausted, but become more vigorous than in their free 

 condition, and reproduce themselves by cell division. As both sym- 

 bionts, the Algae as well as the Fungi, thus derive mutual advantage 

 from their consortism, Lichens form one of the most typical examples 

 of vegetable symbiosis ( 53 ). 



The significance of the Cyanophyceae Nostoc and Awilmfmt in the roots of the 

 Cycadaceae and in the leaves of Azolla and other water plants is still unknown ( M ). 



In connection with these cases of symbiosis between plants, mention may here 

 be made of the similar symbiotic relation existing between animals and plants. 

 Like the Lichen-fungi, lower animals, according to BRANDT, profit by an association 

 with unicellular Algae by appropriating their assimilated products without at the 

 same time disturbing the performance of their functions. Freshwater Polyps 

 (Hydra), Sponges (Spongilla), Ciliata (Stetitor, Paramecium], also Heliozoa, Planaria, 



