CO-OPERATION OF PLANTS. 213 



Each lichen, being comprised of, first, a fungus, made up of a 

 web of myceloid threads, with, second, an alga in its interior, 

 this combination of alga and fungus thus forming the one lichen 

 plant. I must state at this point, to make myself clear, that an 

 alga is a cryptogamic or flowerless plant, without any distinction 

 between stem and leaf, and containing green colouring matter. 

 The ordinary seaweeds are examples of algae, also the green slime 

 found in stagnant water ; but the algae which live in partnership 

 with fungi, forming lichens, are very minute plants, numbers of 

 them being unicellular, but all of them containing green colouring 

 matter inside their cells ; they mostly belonging to the natural 

 order Nostocince. 



The myceloid threads of the fungus being most exterior fulfil 

 the function of gathering from the air moisture, and from the 

 ground or substratum mineral matters ; whilst its partner the alga, 

 owing to its having chlorophyl or green colouring matter, manu- 

 factures starch and other organic chemicals. Thus here again the 

 partners supply each other with matters necessary for the life of 

 both. Then as to the creation of a lichen. A simple experiment 

 will illustrate the facility by which a lichen may be created. If a 

 sheet of white blotting paper moistened with water be exposed for 

 several hours to the wind in the country, and then its surface care- 

 fully examined with a microscope, numerous particles like dust will 

 be found deposited on the paper ; these particles consisting of cell 

 groups of algae, pollen, grains, spores of mosses and fungi, etc. 

 All these bodies would, under natural circumstances, have been 

 deposited in the crevices of the bark of trees, on rocks, stones, etc., 

 and we can easily see, if in these places the little algal cell groups 

 meet with their partner the fungus, the latter will embrace and en- 

 mesh them, and thus create a confederacy known as a lichen. 

 Thus we can easily understand how it is that the bark of trees, 

 rocks exposed to moisture, etc., become clothed with these lichens. 



A most interesting proof of this union is afforded by the fact 

 that a celebrated botanist, M. Bornet, has actually synthesised a 

 lichen — that is, created one. Commencing with certain definite 

 algae, he sowed them, in company with certain definite fungi, in 

 a favourable place. The two separate plants amalgamated and 

 interwove their cells, with the result that a lichen was formed. 



